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 $84.49   9.246%   $92.3019   $92.30   $92.30   $92.30  
  Purchase #2 $92.91   13.110%   $105.0905   $105.09   $105.10   $105.10  
  Purchase #3 $125.64   13.328%   $142.3853   $142.39   $142.40   $142.40  
  Purchase #4 $186.34   10.464%   $205.8386   $205.84   $205.85   $205.80  
  Purchase #5 $210.78   3.239%   $217.6072   $217.61   $217.60   $217.60  
  Purchase #6 $241.93   9.257%   $264.3255   $264.33   $264.35   $264.30  
  Purchase #7 $239.38   6.643%   $255.282   $255.28   $255.30   $255.30  
  7 purchase totals = $1,181.47       $1,282.8310   $1,282.84   $1,282.90   $1,282.80