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 $216.57   7.589%   $233.0055   $233.01   $233.00   $233.00  
  Purchase #2 $202.43   9.193%   $221.0394   $221.04   $221.05   $221.00  
  Purchase #3 $19.57   13.762%   $22.2632   $22.26   $22.25   $22.30  
  Purchase #4 $152.31   6.524%   $162.2467   $162.25   $162.25   $162.20  
  Purchase #5 $87.38   13.726%   $99.3738   $99.37   $99.35   $99.40  
  Purchase #6 $155.41   3.839%   $161.3762   $161.38   $161.40   $161.40  
  Purchase #7 $60.71   12.621%   $68.3722   $68.37   $68.35   $68.40  
  7 purchase totals = $894.38       $967.6770   $967.68   $967.65   $967.70