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 $87.59   7.303%   $93.9867   $93.99   $94.00   $94.00  
  Purchase #2 $30.51   12.397%   $34.2923   $34.29   $34.30   $34.30  
  Purchase #3 $106.94   13.291%   $121.1534   $121.15   $121.15   $121.20  
  Purchase #4 $41.28   7.317%   $44.3005   $44.30   $44.30   $44.30  
  Purchase #5 $151.84   8.588%   $164.88   $164.88   $164.90   $164.90  
  Purchase #6 $249.96   11.289%   $278.178   $278.18   $278.20   $278.20  
  Purchase #7 $224.44   12.864%   $253.312   $253.31   $253.30   $253.30  
  7 purchase totals = $892.56       $990.1029   $990.10   $990.15   $990.20