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 $20.54   5.484%   $21.6664   $21.67   $21.65   $21.70  
  Purchase #2 $12.58   4.205%   $13.109   $13.11   $13.10   $13.10  
  Purchase #3 $90.80   12.754%   $102.3806   $102.38   $102.40   $102.40  
  Purchase #4 $151.83   10.440%   $167.6811   $167.68   $167.70   $167.70  
  Purchase #5 $67.28   13.413%   $76.3043   $76.30   $76.30   $76.30  
  Purchase #6 $100.30   4.118%   $104.4304   $104.43   $104.45   $104.40  
  Purchase #7 $221.97   13.385%   $251.6807   $251.68   $251.70   $251.70  
  7 purchase totals = $665.30       $737.2525   $737.25   $737.30   $737.30