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 $89.67   6.502%   $95.5003   $95.50   $95.50   $95.50  
  Purchase #2 $24.67   9.276%   $26.9584   $26.96   $26.95   $27.00  
  Purchase #3 $86.32   9.804%   $94.7828   $94.78   $94.80   $94.80  
  Purchase #4 $208.76   7.636%   $224.7009   $224.70   $224.70   $224.70  
  Purchase #5 $14.90   13.530%   $16.916   $16.92   $16.90   $16.90  
  Purchase #6 $205.62   10.398%   $227.0004   $227.00   $227.00   $227.00  
  Purchase #7 $133.26   12.725%   $150.2173   $150.22   $150.20   $150.20  
  7 purchase totals = $763.20       $836.0761   $836.08   $836.05   $836.10