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 $236.42   10.462%   $261.1543   $261.15   $261.15   $261.20  
  Purchase #2 $169.64   5.767%   $179.4231   $179.42   $179.40   $179.40  
  Purchase #3 $88.40   4.418%   $92.3055   $92.31   $92.30   $92.30  
  Purchase #4 $40.53   9.851%   $44.5226   $44.52   $44.50   $44.50  
  Purchase #5 $164.63   8.653%   $178.8754   $178.88   $178.90   $178.90  
  Purchase #6 $119.71   10.275%   $132.0102   $132.01   $132.00   $132.00  
  Purchase #7 $97.63   8.830%   $106.2507   $106.25   $106.25   $106.30  
  7 purchase totals = $916.96       $994.5418   $994.54   $994.50   $994.60