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 $36.58   12.634%   $41.2015   $41.20   $41.20   $41.20  
  Purchase #2 $199.87   9.617%   $219.0915   $219.09   $219.10   $219.10  
  Purchase #3 $157.72   8.340%   $170.8738   $170.87   $170.85   $170.90  
  Purchase #4 $194.60   7.555%   $209.302   $209.30   $209.30   $209.30  
  Purchase #5 $238.46   9.799%   $261.8267   $261.83   $261.85   $261.80  
  Purchase #6 $17.86   11.253%   $19.8698   $19.87   $19.85   $19.90  
  Purchase #7 $81.28   11.358%   $90.5118   $90.51   $90.50   $90.50  
  7 purchase totals = $926.37       $1,012.6771   $1,012.67   $1,012.65   $1,012.70