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 $82.79   4.257%   $86.3144   $86.31   $86.30   $86.30  
  Purchase #2 $146.71   12.594%   $165.1867   $165.19   $165.20   $165.20  
  Purchase #3 $45.38   9.543%   $49.7106   $49.71   $49.70   $49.70  
  Purchase #4 $24.92   13.120%   $28.1895   $28.19   $28.20   $28.20  
  Purchase #5 $119.80   13.267%   $135.6939   $135.69   $135.70   $135.70  
  Purchase #6 $154.41   8.350%   $167.3032   $167.30   $167.30   $167.30  
  Purchase #7 $243.78   4.696%   $255.2279   $255.23   $255.25   $255.20  
  7 purchase totals = $817.79       $887.6262   $887.62   $887.65   $887.60