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 $56.95   7.552%   $61.2509   $61.25   $61.25   $61.30  
  Purchase #2 $92.25   9.734%   $101.2296   $101.23   $101.25   $101.20  
  Purchase #3 $109.44   5.637%   $115.6091   $115.61   $115.60   $115.60  
  Purchase #4 $53.49   9.840%   $58.7534   $58.75   $58.75   $58.80  
  Purchase #5 $153.26   10.601%   $169.5071   $169.51   $169.50   $169.50  
  Purchase #6 $146.28   3.313%   $151.1263   $151.13   $151.15   $151.10  
  Purchase #7 $45.69   8.527%   $49.586   $49.59   $49.60   $49.60  
  7 purchase totals = $657.36       $707.0624   $707.07   $707.10   $707.10