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 $164.44   9.653%   $180.3134   $180.31   $180.30   $180.30  
  Purchase #2 $125.82   6.608%   $134.1342   $134.13   $134.15   $134.10  
  Purchase #3 $139.68   6.347%   $148.5455   $148.55   $148.55   $148.50  
  Purchase #4 $194.91   10.621%   $215.6114   $215.61   $215.60   $215.60  
  Purchase #5 $178.85   4.142%   $186.258   $186.26   $186.25   $186.30  
  Purchase #6 $29.76   3.185%   $30.7079   $30.71   $30.70   $30.70  
  Purchase #7 $129.84   4.393%   $135.5439   $135.54   $135.55   $135.50  
  7 purchase totals = $963.30       $1,031.1143   $1,031.11   $1,031.10   $1,031.00