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 $230.92   11.127%   $256.6145   $256.61   $256.60   $256.60  
  Purchase #2 $92.45   5.644%   $97.6679   $97.67   $97.65   $97.70  
  Purchase #3 $215.57   13.399%   $244.4542   $244.45   $244.45   $244.50  
  Purchase #4 $25.56   5.426%   $26.9469   $26.95   $26.95   $26.90  
  Purchase #5 $40.55   3.479%   $41.9607   $41.96   $41.95   $42.00  
  Purchase #6 $60.31   13.727%   $68.5888   $68.59   $68.60   $68.60  
  Purchase #7 $142.77   12.278%   $160.2993   $160.30   $160.30   $160.30  
  7 purchase totals = $808.13       $896.5323   $896.53   $896.50   $896.60