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 $94.69   3.220%   $97.739   $97.74   $97.75   $97.70  
  Purchase #2 $187.97   8.109%   $203.2125   $203.21   $203.20   $203.20  
  Purchase #3 $162.40   4.146%   $169.1331   $169.13   $169.15   $169.10  
  Purchase #4 $61.57   8.439%   $66.7659   $66.77   $66.75   $66.80  
  Purchase #5 $205.94   12.862%   $232.428   $232.43   $232.45   $232.40  
  Purchase #6 $60.42   4.141%   $62.922   $62.92   $62.90   $62.90  
  Purchase #7 $186.71   6.595%   $199.0235   $199.02   $199.00   $199.00  
  7 purchase totals = $959.70       $1,031.2240   $1,031.22   $1,031.20   $1,031.10