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 $173.41   12.290%   $194.7221   $194.72   $194.70   $194.70  
  Purchase #2 $131.98   6.286%   $140.2763   $140.28   $140.30   $140.30  
  Purchase #3 $132.40   12.822%   $149.3763   $149.38   $149.40   $149.40  
  Purchase #4 $9.72   6.227%   $10.3253   $10.33   $10.35   $10.30  
  Purchase #5 $185.40   5.681%   $195.9326   $195.93   $195.95   $195.90  
  Purchase #6 $233.54   6.838%   $249.5095   $249.51   $249.50   $249.50  
  Purchase #7 $84.93   13.243%   $96.1773   $96.18   $96.20   $96.20  
  7 purchase totals = $951.38       $1,036.3194   $1,036.33   $1,036.40   $1,036.30