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 $58.92   8.534%   $63.9482   $63.95   $63.95   $63.90  
  Purchase #2 $153.57   10.340%   $169.4491   $169.45   $169.45   $169.40  
  Purchase #3 $168.51   5.421%   $177.6449   $177.64   $177.65   $177.60  
  Purchase #4 $16.76   9.586%   $18.3666   $18.37   $18.35   $18.40  
  Purchase #5 $158.31   6.500%   $168.6002   $168.60   $168.60   $168.60  
  Purchase #6 $162.82   4.613%   $170.3309   $170.33   $170.35   $170.30  
  Purchase #7 $250.94   7.699%   $270.2599   $270.26   $270.25   $270.30  
  7 purchase totals = $969.83       $1,038.5998   $1,038.60   $1,038.60   $1,038.50