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 $181.34   13.281%   $205.4238   $205.42   $205.40   $205.40  
  Purchase #2 $11.39   4.610%   $11.9151   $11.92   $11.90   $11.90  
  Purchase #3 $60.40   7.237%   $64.7711   $64.77   $64.75   $64.80  
  Purchase #4 $202.94   4.574%   $212.2225   $212.22   $212.20   $212.20  
  Purchase #5 $78.28   9.350%   $85.5992   $85.60   $85.60   $85.60  
  Purchase #6 $217.99   10.391%   $240.6413   $240.64   $240.65   $240.60  
  Purchase #7 $132.47   6.727%   $141.3813   $141.38   $141.40   $141.40  
  7 purchase totals = $884.81       $961.9543   $961.95   $961.90   $961.90