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 $119.25   10.761%   $132.0825   $132.08   $132.10   $132.10  
  Purchase #2 $163.56   7.266%   $175.4443   $175.44   $175.45   $175.40  
  Purchase #3 $116.96   5.441%   $123.3238   $123.32   $123.30   $123.30  
  Purchase #4 $245.66   5.661%   $259.5668   $259.57   $259.55   $259.60  
  Purchase #5 $223.90   5.532%   $236.2861   $236.29   $236.30   $236.30  
  Purchase #6 $17.40   11.191%   $19.3472   $19.35   $19.35   $19.30  
  Purchase #7 $26.66   10.811%   $29.5422   $29.54   $29.55   $29.50  
  7 purchase totals = $913.39       $975.5929   $975.59   $975.60   $975.50