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 $173.83   12.613%   $195.7552   $195.76   $195.75   $195.80  
  Purchase #2 $182.42   12.575%   $205.3593   $205.36   $205.35   $205.40  
  Purchase #3 $174.37   11.367%   $194.1906   $194.19   $194.20   $194.20  
  Purchase #4 $82.46   3.721%   $85.5283   $85.53   $85.55   $85.50  
  Purchase #5 $27.86   6.337%   $29.6255   $29.63   $29.65   $29.60  
  Purchase #6 $168.60   3.154%   $173.9176   $173.92   $173.90   $173.90  
  Purchase #7 $13.27   7.296%   $14.2382   $14.24   $14.25   $14.20  
  7 purchase totals = $822.81       $898.6147   $898.63   $898.65   $898.60