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 $218.88   10.853%   $242.635   $242.64   $242.65   $242.60  
  Purchase #2 $21.40   9.390%   $23.4095   $23.41   $23.40   $23.40  
  Purchase #3 $158.68   9.237%   $173.3373   $173.34   $173.35   $173.30  
  Purchase #4 $53.39   3.559%   $55.2902   $55.29   $55.30   $55.30  
  Purchase #5 $250.86   3.290%   $259.1133   $259.11   $259.10   $259.10  
  Purchase #6 $234.89   6.430%   $249.9934   $249.99   $250.00   $250.00  
  Purchase #7 $58.78   13.687%   $66.8252   $66.83   $66.85   $66.80  
  7 purchase totals = $996.88       $1,070.6039   $1,070.61   $1,070.65   $1,070.50