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 $184.81   11.318%   $205.7268   $205.73   $205.75   $205.70  
  Purchase #2 $8.34   4.109%   $8.6827   $8.68   $8.70   $8.70  
  Purchase #3 $24.38   4.256%   $25.4176   $25.42   $25.40   $25.40  
  Purchase #4 $195.57   6.178%   $207.6523   $207.65   $207.65   $207.70  
  Purchase #5 $215.27   10.672%   $238.2436   $238.24   $238.25   $238.20  
  Purchase #6 $34.25   5.671%   $36.1923   $36.19   $36.20   $36.20  
  Purchase #7 $65.89   5.314%   $69.3914   $69.39   $69.40   $69.40  
  7 purchase totals = $728.51       $791.3067   $791.30   $791.35   $791.30