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 $231.47   9.400%   $253.2282   $253.23   $253.25   $253.20  
  Purchase #2 $32.46   6.405%   $34.5391   $34.54   $34.55   $34.50  
  Purchase #3 $170.91   11.498%   $190.5612   $190.56   $190.55   $190.60  
  Purchase #4 $245.84   13.569%   $279.198   $279.20   $279.20   $279.20  
  Purchase #5 $34.80   3.291%   $35.9453   $35.95   $35.95   $35.90  
  Purchase #6 $68.65   9.450%   $75.1374   $75.14   $75.15   $75.10  
  Purchase #7 $183.87   6.165%   $195.2056   $195.21   $195.20   $195.20  
  7 purchase totals = $968.00       $1,063.8148   $1,063.83   $1,063.85   $1,063.70