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 $85.27   10.828%   $94.503   $94.50   $94.50   $94.50  
  Purchase #2 $101.71   9.390%   $111.2606   $111.26   $111.25   $111.30  
  Purchase #3 $9.52   7.570%   $10.2407   $10.24   $10.25   $10.20  
  Purchase #4 $130.53   5.587%   $137.8227   $137.82   $137.80   $137.80  
  Purchase #5 $203.83   7.628%   $219.3782   $219.38   $219.40   $219.40  
  Purchase #6 $175.75   6.595%   $187.3407   $187.34   $187.35   $187.30  
  Purchase #7 $114.53   6.290%   $121.7339   $121.73   $121.75   $121.70  
  7 purchase totals = $821.14       $882.2798   $882.27   $882.30   $882.20