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 $48.50   12.428%   $54.5276   $54.53   $54.55   $54.50  
  Purchase #2 $67.27   10.617%   $74.4121   $74.41   $74.40   $74.40  
  Purchase #3 $224.39   5.272%   $236.2198   $236.22   $236.20   $236.20  
  Purchase #4 $120.39   3.244%   $124.2955   $124.30   $124.30   $124.30  
  Purchase #5 $171.99   13.457%   $195.1347   $195.13   $195.15   $195.10  
  Purchase #6 $164.27   6.802%   $175.4436   $175.44   $175.45   $175.40  
  Purchase #7 $179.51   13.564%   $203.8587   $203.86   $203.85   $203.90  
  7 purchase totals = $976.32       $1,063.8920   $1,063.89   $1,063.90   $1,063.80