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 $209.54   11.130%   $232.8618   $232.86   $232.85   $232.90  
  Purchase #2 $201.37   8.836%   $219.1631   $219.16   $219.15   $219.20  
  Purchase #3 $62.35   3.523%   $64.5466   $64.55   $64.55   $64.50  
  Purchase #4 $90.37   5.494%   $95.3349   $95.33   $95.35   $95.30  
  Purchase #5 $169.80   6.419%   $180.6995   $180.70   $180.70   $180.70  
  Purchase #6 $59.69   8.616%   $64.8329   $64.83   $64.85   $64.80  
  Purchase #7 $137.57   6.585%   $146.629   $146.63   $146.65   $146.60  
  7 purchase totals = $930.69       $1,004.0678   $1,004.06   $1,004.10   $1,004.00