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 $54.78   12.231%   $61.4801   $61.48   $61.50   $61.50  
  Purchase #2 $167.68   13.178%   $189.7769   $189.78   $189.80   $189.80  
  Purchase #3 $119.69   11.333%   $133.2545   $133.25   $133.25   $133.30  
  Purchase #4 $225.51   4.186%   $234.9498   $234.95   $234.95   $234.90  
  Purchase #5 $224.74   8.304%   $243.4024   $243.40   $243.40   $243.40  
  Purchase #6 $226.58   10.188%   $249.664   $249.66   $249.65   $249.70  
  Purchase #7 $206.86   8.498%   $224.439   $224.44   $224.45   $224.40  
  7 purchase totals = $1,225.84       $1,336.9667   $1,336.96   $1,337.00   $1,337.00