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 $135.33   12.650%   $152.4492   $152.45   $152.45   $152.40  
  Purchase #2 $71.72   4.519%   $74.961   $74.96   $74.95   $75.00  
  Purchase #3 $54.63   4.524%   $57.1015   $57.10   $57.10   $57.10  
  Purchase #4 $182.48   7.283%   $195.77   $195.77   $195.75   $195.80  
  Purchase #5 $88.92   4.203%   $92.6573   $92.66   $92.65   $92.70  
  Purchase #6 $94.47   3.349%   $97.6338   $97.63   $97.65   $97.60  
  Purchase #7 $245.57   11.123%   $272.8848   $272.88   $272.90   $272.90  
  7 purchase totals = $873.12       $943.4576   $943.45   $943.45   $943.50