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 $204.75   10.164%   $225.5608   $225.56   $225.55   $225.60  
  Purchase #2 $112.82   8.166%   $122.0329   $122.03   $122.05   $122.00  
  Purchase #3 $117.88   10.351%   $130.0818   $130.08   $130.10   $130.10  
  Purchase #4 $70.38   12.741%   $79.3471   $79.35   $79.35   $79.30  
  Purchase #5 $240.92   6.772%   $257.2351   $257.24   $257.25   $257.20  
  Purchase #6 $13.70   4.192%   $14.2743   $14.27   $14.25   $14.30  
  Purchase #7 $185.96   13.130%   $210.3765   $210.38   $210.40   $210.40  
  7 purchase totals = $946.41       $1,038.9085   $1,038.91   $1,038.95   $1,038.90