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 $43.97   5.546%   $46.4086   $46.41   $46.40   $46.40  
  Purchase #2 $99.83   4.786%   $104.6079   $104.61   $104.60   $104.60  
  Purchase #3 $85.65   10.846%   $94.9396   $94.94   $94.95   $94.90  
  Purchase #4 $74.52   5.314%   $78.48   $78.48   $78.50   $78.50  
  Purchase #5 $209.37   5.562%   $221.0152   $221.02   $221.00   $221.00  
  Purchase #6 $103.45   4.339%   $107.9387   $107.94   $107.95   $107.90  
  Purchase #7 $86.55   11.725%   $96.698   $96.70   $96.70   $96.70  
  7 purchase totals = $703.34       $750.0880   $750.10   $750.10   $750.00