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 $226.99   12.623%   $255.6429   $255.64   $255.65   $255.60  
  Purchase #2 $48.60   5.677%   $51.359   $51.36   $51.35   $51.40  
  Purchase #3 $216.48   7.417%   $232.5363   $232.54   $232.55   $232.50  
  Purchase #4 $200.49   12.292%   $225.1342   $225.13   $225.15   $225.10  
  Purchase #5 $188.71   9.315%   $206.2883   $206.29   $206.30   $206.30  
  Purchase #6 $57.34   8.738%   $62.3504   $62.35   $62.35   $62.40  
  Purchase #7 $154.34   7.109%   $165.312   $165.31   $165.30   $165.30  
  7 purchase totals = $1,092.95       $1,198.6231   $1,198.62   $1,198.65   $1,198.60