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 $249.49   8.142%   $269.8035   $269.80   $269.80   $269.80  
  Purchase #2 $230.79   12.562%   $259.7818   $259.78   $259.80   $259.80  
  Purchase #3 $162.40   6.867%   $173.552   $173.55   $173.55   $173.60  
  Purchase #4 $20.34   10.518%   $22.4794   $22.48   $22.50   $22.50  
  Purchase #5 $93.71   6.856%   $100.1348   $100.13   $100.15   $100.10  
  Purchase #6 $177.94   3.172%   $183.5843   $183.58   $183.60   $183.60  
  Purchase #7 $229.74   11.546%   $256.2658   $256.27   $256.25   $256.30  
  7 purchase totals = $1,164.41       $1,265.6016   $1,265.59   $1,265.65   $1,265.70