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 $237.66   12.428%   $267.1964   $267.20   $267.20   $267.20  
  Purchase #2 $72.98   13.868%   $83.1009   $83.10   $83.10   $83.10  
  Purchase #3 $105.71   12.487%   $118.91   $118.91   $118.90   $118.90  
  Purchase #4 $230.64   7.484%   $247.9011   $247.90   $247.90   $247.90  
  Purchase #5 $32.54   3.232%   $33.5917   $33.59   $33.60   $33.60  
  Purchase #6 $114.76   12.390%   $128.9788   $128.98   $129.00   $129.00  
  Purchase #7 $14.25   6.373%   $15.1582   $15.16   $15.15   $15.20  
  7 purchase totals = $808.54       $894.8371   $894.84   $894.85   $894.90