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 $235.87   11.302%   $262.528   $262.53   $262.55   $262.50  
  Purchase #2 $125.51   12.105%   $140.703   $140.70   $140.70   $140.70  
  Purchase #3 $243.43   13.371%   $275.979   $275.98   $276.00   $276.00  
  Purchase #4 $56.97   7.475%   $61.2285   $61.23   $61.25   $61.20  
  Purchase #5 $150.28   5.874%   $159.1074   $159.11   $159.10   $159.10  
  Purchase #6 $57.43   11.455%   $64.0086   $64.01   $64.00   $64.00  
  Purchase #7 $184.39   3.336%   $190.5413   $190.54   $190.55   $190.50  
  7 purchase totals = $1,053.88       $1,154.0958   $1,154.10   $1,154.15   $1,154.00