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 $74.76   13.579%   $84.9117   $84.91   $84.90   $84.90  
  Purchase #2 $96.31   7.309%   $103.3493   $103.35   $103.35   $103.30  
  Purchase #3 $93.39   10.196%   $102.912   $102.91   $102.90   $102.90  
  Purchase #4 $94.30   3.873%   $97.9522   $97.95   $97.95   $98.00  
  Purchase #5 $229.85   11.353%   $255.9449   $255.94   $255.95   $255.90  
  Purchase #6 $131.69   11.342%   $146.6263   $146.63   $146.65   $146.60  
  Purchase #7 $30.40   11.787%   $33.9832   $33.98   $34.00   $34.00  
  7 purchase totals = $750.70       $825.6796   $825.67   $825.70   $825.60