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 $66.86   11.551%   $74.583   $74.58   $74.60   $74.60  
  Purchase #2 $70.38   9.745%   $77.2385   $77.24   $77.25   $77.20  
  Purchase #3 $218.47   12.614%   $246.0278   $246.03   $246.05   $246.00  
  Purchase #4 $211.53   5.520%   $223.2065   $223.21   $223.20   $223.20  
  Purchase #5 $44.60   4.804%   $46.7426   $46.74   $46.75   $46.70  
  Purchase #6 $215.44   11.739%   $240.7305   $240.73   $240.75   $240.70  
  Purchase #7 $90.48   4.185%   $94.2666   $94.27   $94.25   $94.30  
  7 purchase totals = $917.76       $1,002.7955   $1,002.80   $1,002.85   $1,002.70