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 $197.79   4.150%   $205.9983   $206.00   $206.00   $206.00  
  Purchase #2 $162.49   9.585%   $178.0647   $178.06   $178.05   $178.10  
  Purchase #3 $154.63   12.441%   $173.8675   $173.87   $173.85   $173.90  
  Purchase #4 $237.76   12.853%   $268.3193   $268.32   $268.30   $268.30  
  Purchase #5 $213.26   7.252%   $228.7256   $228.73   $228.75   $228.70  
  Purchase #6 $12.41   11.604%   $13.8501   $13.85   $13.85   $13.90  
  Purchase #7 $187.66   9.171%   $204.8703   $204.87   $204.85   $204.90  
  7 purchase totals = $1,166.00       $1,273.6958   $1,273.70   $1,273.65   $1,273.80