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 $79.47   11.185%   $88.3587   $88.36   $88.35   $88.40  
  Purchase #2 $58.67   10.827%   $65.0222   $65.02   $65.00   $65.00  
  Purchase #3 $153.87   12.172%   $172.5991   $172.60   $172.60   $172.60  
  Purchase #4 $180.55   7.203%   $193.555   $193.56   $193.55   $193.60  
  Purchase #5 $86.53   12.525%   $97.3679   $97.37   $97.35   $97.40  
  Purchase #6 $236.65   7.811%   $255.1347   $255.13   $255.15   $255.10  
  Purchase #7 $70.69   5.845%   $74.8218   $74.82   $74.80   $74.80  
  7 purchase totals = $866.43       $946.8594   $946.86   $946.80   $946.90