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 $58.79   6.595%   $62.6672   $62.67   $62.65   $62.70  
  Purchase #2 $171.60   11.146%   $190.7265   $190.73   $190.75   $190.70  
  Purchase #3 $160.85   5.352%   $169.4587   $169.46   $169.45   $169.50  
  Purchase #4 $11.68   9.303%   $12.7666   $12.77   $12.75   $12.80  
  Purchase #5 $150.47   6.754%   $160.6327   $160.63   $160.65   $160.60  
  Purchase #6 $8.92   4.442%   $9.3162   $9.32   $9.30   $9.30  
  Purchase #7 $187.74   12.403%   $211.0254   $211.03   $211.05   $211.00  
  7 purchase totals = $750.05       $816.5933   $816.61   $816.60   $816.60