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 $7.51   4.624%   $7.8573   $7.86   $7.85   $7.90  
  Purchase #2 $146.77   12.168%   $164.629   $164.63   $164.65   $164.60  
  Purchase #3 $114.30   10.303%   $126.0763   $126.08   $126.10   $126.10  
  Purchase #4 $138.90   3.228%   $143.3837   $143.38   $143.40   $143.40  
  Purchase #5 $205.53   7.605%   $221.1606   $221.16   $221.15   $221.20  
  Purchase #6 $36.55   7.819%   $39.4078   $39.41   $39.40   $39.40  
  Purchase #7 $164.54   9.538%   $180.2338   $180.23   $180.25   $180.20  
  7 purchase totals = $814.10       $882.7485   $882.75   $882.80   $882.80