Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $215.90   13.168%   $244.3297   $244.33   $244.35   $244.30  
  Purchase #2 $156.94   10.649%   $173.6525   $173.65   $173.65   $173.70  
  Purchase #3 $175.30   8.118%   $189.5309   $189.53   $189.55   $189.50  
  Purchase #4 $237.69   11.340%   $264.644   $264.64   $264.65   $264.60  
  Purchase #5 $240.92   12.328%   $270.6206   $270.62   $270.60   $270.60  
  Purchase #6 $201.49   4.655%   $210.8694   $210.87   $210.85   $210.90  
  Purchase #7 $100.90   13.763%   $114.7869   $114.79   $114.80   $114.80  
  7 purchase totals = $1,329.14       $1,468.4340   $1,468.43   $1,468.45   $1,468.40