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 $44.84   10.657%   $49.6186   $49.62   $49.60   $49.60  
  Purchase #2 $143.92   12.167%   $161.4307   $161.43   $161.45   $161.40  
  Purchase #3 $111.28   4.184%   $115.936   $115.94   $115.95   $115.90  
  Purchase #4 $128.80   3.295%   $133.044   $133.04   $133.05   $133.00  
  Purchase #5 $85.89   9.339%   $93.9113   $93.91   $93.90   $93.90  
  Purchase #6 $151.63   9.504%   $166.0409   $166.04   $166.05   $166.00  
  Purchase #7 $224.71   13.562%   $255.1852   $255.19   $255.20   $255.20  
  7 purchase totals = $891.07       $975.1667   $975.17   $975.20   $975.00