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   9.618%   $64.5869   $64.59   $64.60   $64.60  
  Purchase #2 $201.44   8.809%   $219.1848   $219.18   $219.20   $219.20  
  Purchase #3 $22.41   7.480%   $24.0863   $24.09   $24.10   $24.10  
  Purchase #4 $69.48   5.480%   $73.2875   $73.29   $73.30   $73.30  
  Purchase #5 $44.99   12.600%   $50.6587   $50.66   $50.65   $50.70  
  Purchase #6 $149.40   13.282%   $169.2433   $169.24   $169.25   $169.20  
  Purchase #7 $178.97   11.720%   $199.9453   $199.95   $199.95   $199.90  
  7 purchase totals = $725.61       $800.9928   $801.00   $801.05   $801.00