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 $53.99   11.634%   $60.2712   $60.27   $60.25   $60.30  
  Purchase #2 $114.58   8.511%   $124.3319   $124.33   $124.35   $124.30  
  Purchase #3 $42.86   7.452%   $46.0539   $46.05   $46.05   $46.10  
  Purchase #4 $120.87   7.379%   $129.789   $129.79   $129.80   $129.80  
  Purchase #5 $103.45   5.551%   $109.1925   $109.19   $109.20   $109.20  
  Purchase #6 $180.75   9.227%   $197.4278   $197.43   $197.45   $197.40  
  Purchase #7 $69.58   6.109%   $73.8306   $73.83   $73.85   $73.80  
  7 purchase totals = $686.08       $740.8969   $740.89   $740.95   $740.90