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 $160.27   11.335%   $178.4366   $178.44   $178.45   $178.40  
  Purchase #2 $242.95   13.345%   $275.3717   $275.37   $275.35   $275.40  
  Purchase #3 $245.85   8.309%   $266.2777   $266.28   $266.30   $266.30  
  Purchase #4 $22.83   8.380%   $24.7432   $24.74   $24.75   $24.70  
  Purchase #5 $11.73   9.491%   $12.8433   $12.84   $12.85   $12.80  
  Purchase #6 $56.87   13.128%   $64.3359   $64.34   $64.35   $64.30  
  Purchase #7 $133.59   3.129%   $137.77   $137.77   $137.75   $137.80  
  7 purchase totals = $874.09       $959.7784   $959.78   $959.80   $959.70