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 $59.74   12.214%   $67.0366   $67.04   $67.05   $67.00  
  Purchase #2 $38.62   13.130%   $43.6908   $43.69   $43.70   $43.70  
  Purchase #3 $83.27   11.166%   $92.5679   $92.57   $92.55   $92.60  
  Purchase #4 $114.89   13.324%   $130.1979   $130.20   $130.20   $130.20  
  Purchase #5 $55.68   7.316%   $59.7535   $59.75   $59.75   $59.80  
  Purchase #6 $243.51   9.748%   $267.2474   $267.25   $267.25   $267.20  
  Purchase #7 $243.73   4.290%   $254.186   $254.19   $254.20   $254.20  
  7 purchase totals = $839.44       $914.6801   $914.69   $914.70   $914.70