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 $238.57   10.692%   $264.0779   $264.08   $264.10   $264.10  
  Purchase #2 $207.96   4.373%   $217.0541   $217.05   $217.05   $217.10  
  Purchase #3 $46.40   5.248%   $48.8351   $48.84   $48.85   $48.80  
  Purchase #4 $22.87   8.622%   $24.8419   $24.84   $24.85   $24.80  
  Purchase #5 $241.61   12.832%   $272.6134   $272.61   $272.60   $272.60  
  Purchase #6 $244.99   3.436%   $253.4079   $253.41   $253.40   $253.40  
  Purchase #7 $154.75   7.722%   $166.6998   $166.70   $166.70   $166.70  
  7 purchase totals = $1,157.15       $1,247.5301   $1,247.53   $1,247.55   $1,247.50