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 $154.59   13.527%   $175.5014   $175.50   $175.50   $175.50  
  Purchase #2 $111.95   11.812%   $125.1735   $125.17   $125.15   $125.20  
  Purchase #3 $38.77   5.776%   $41.0094   $41.01   $41.00   $41.00  
  Purchase #4 $18.48   10.638%   $20.4459   $20.45   $20.45   $20.40  
  Purchase #5 $114.86   5.776%   $121.4943   $121.49   $121.50   $121.50  
  Purchase #6 $114.73   12.335%   $128.8819   $128.88   $128.90   $128.90  
  Purchase #7 $241.39   11.135%   $268.2688   $268.27   $268.25   $268.30  
  7 purchase totals = $794.77       $880.7752   $880.77   $880.75   $880.80