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 $64.26   3.733%   $66.6588   $66.66   $66.65   $66.70  
  Purchase #2 $22.44   5.781%   $23.7373   $23.74   $23.75   $23.70  
  Purchase #3 $143.81   7.712%   $154.9006   $154.90   $154.90   $154.90  
  Purchase #4 $125.31   11.754%   $140.0389   $140.04   $140.05   $140.00  
  Purchase #5 $206.27   5.461%   $217.5344   $217.53   $217.55   $217.50  
  Purchase #6 $60.58   11.414%   $67.4946   $67.49   $67.50   $67.50  
  Purchase #7 $156.66   4.160%   $163.1771   $163.18   $163.20   $163.20  
  7 purchase totals = $779.33       $833.5417   $833.54   $833.60   $833.50