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 $219.54   13.683%   $249.5797   $249.58   $249.60   $249.60  
  Purchase #2 $189.89   9.166%   $207.2953   $207.30   $207.30   $207.30  
  Purchase #3 $204.59   6.425%   $217.7349   $217.73   $217.75   $217.70  
  Purchase #4 $194.37   5.706%   $205.4608   $205.46   $205.45   $205.50  
  Purchase #5 $189.73   5.296%   $199.7781   $199.78   $199.80   $199.80  
  Purchase #6 $92.46   6.283%   $98.2693   $98.27   $98.25   $98.30  
  Purchase #7 $59.93   6.152%   $63.6169   $63.62   $63.60   $63.60  
  7 purchase totals = $1,150.51       $1,241.7350   $1,241.74   $1,241.75   $1,241.80