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 $137.33   11.432%   $153.0296   $153.03   $153.05   $153.00  
  Purchase #2 $87.72   11.226%   $97.5674   $97.57   $97.55   $97.60  
  Purchase #3 $95.38   6.404%   $101.4881   $101.49   $101.50   $101.50  
  Purchase #4 $120.53   7.164%   $129.1648   $129.16   $129.15   $129.20  
  Purchase #5 $19.83   10.140%   $21.8408   $21.84   $21.85   $21.80  
  Purchase #6 $234.63   11.321%   $261.1925   $261.19   $261.20   $261.20  
  Purchase #7 $227.42   4.336%   $237.2809   $237.28   $237.30   $237.30  
  7 purchase totals = $922.84       $1,001.5641   $1,001.56   $1,001.60   $1,001.60