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 $57.85   9.120%   $63.1259   $63.13   $63.15   $63.10  
  Purchase #2 $58.38   10.665%   $64.6062   $64.61   $64.60   $64.60  
  Purchase #3 $152.92   13.148%   $173.0259   $173.03   $173.05   $173.00  
  Purchase #4 $211.42   7.404%   $227.0735   $227.07   $227.05   $227.10  
  Purchase #5 $9.55   7.424%   $10.259   $10.26   $10.25   $10.30  
  Purchase #6 $154.73   10.142%   $170.4227   $170.42   $170.40   $170.40  
  Purchase #7 $185.37   5.225%   $195.0556   $195.06   $195.05   $195.10  
  7 purchase totals = $830.22       $903.5688   $903.58   $903.55   $903.60