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 $144.25   7.401%   $154.9259   $154.93   $154.95   $154.90  
  Purchase #2 $57.95   8.107%   $62.648   $62.65   $62.65   $62.60  
  Purchase #3 $76.67   9.130%   $83.67   $83.67   $83.65   $83.70  
  Purchase #4 $233.96   5.469%   $246.7553   $246.76   $246.75   $246.80  
  Purchase #5 $241.38   8.151%   $261.0549   $261.05   $261.05   $261.10  
  Purchase #6 $42.87   3.176%   $44.2316   $44.23   $44.25   $44.20  
  Purchase #7 $114.95   11.666%   $128.3601   $128.36   $128.35   $128.40  
  7 purchase totals = $912.03       $981.6458   $981.65   $981.65   $981.70