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 $82.51   11.177%   $91.7321   $91.73   $91.75   $91.70  
  Purchase #2 $11.55   8.461%   $12.5272   $12.53   $12.55   $12.50  
  Purchase #3 $212.47   12.603%   $239.2476   $239.25   $239.25   $239.20  
  Purchase #4 $59.73   13.393%   $67.7296   $67.73   $67.75   $67.70  
  Purchase #5 $54.67   9.570%   $59.9019   $59.90   $59.90   $59.90  
  Purchase #6 $212.26   4.468%   $221.7438   $221.74   $221.75   $221.70  
  Purchase #7 $231.98   9.312%   $253.582   $253.58   $253.60   $253.60  
  7 purchase totals = $865.17       $946.4642   $946.46   $946.55   $946.30