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 $81.41   8.787%   $88.5635   $88.56   $88.55   $88.60  
  Purchase #2 $188.79   8.574%   $204.9769   $204.98   $205.00   $205.00  
  Purchase #3 $244.63   3.475%   $253.1309   $253.13   $253.15   $253.10  
  Purchase #4 $249.75   13.605%   $283.7285   $283.73   $283.75   $283.70  
  Purchase #5 $154.83   5.182%   $162.8533   $162.85   $162.85   $162.90  
  Purchase #6 $103.95   8.131%   $112.4022   $112.40   $112.40   $112.40  
  Purchase #7 $246.57   11.475%   $274.8639   $274.86   $274.85   $274.90  
  7 purchase totals = $1,269.93       $1,380.5192   $1,380.51   $1,380.55   $1,380.60