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 $231.50   13.708%   $263.234   $263.23   $263.25   $263.20  
  Purchase #2 $106.83   13.244%   $120.9786   $120.98   $121.00   $121.00  
  Purchase #3 $79.27   6.406%   $84.348   $84.35   $84.35   $84.30  
  Purchase #4 $34.81   8.157%   $37.6495   $37.65   $37.65   $37.60  
  Purchase #5 $119.57   4.807%   $125.3177   $125.32   $125.30   $125.30  
  Purchase #6 $172.53   8.414%   $187.0467   $187.05   $187.05   $187.00  
  Purchase #7 $160.67   5.396%   $169.3398   $169.34   $169.35   $169.30  
  7 purchase totals = $905.18       $987.9143   $987.92   $987.95   $987.70