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 $209.32   11.682%   $233.7728   $233.77   $233.75   $233.80  
  Purchase #2 $243.36   12.193%   $273.0329   $273.03   $273.05   $273.00  
  Purchase #3 $48.86   12.205%   $54.8234   $54.82   $54.80   $54.80  
  Purchase #4 $126.90   5.337%   $133.6727   $133.67   $133.65   $133.70  
  Purchase #5 $247.47   8.811%   $269.2746   $269.27   $269.25   $269.30  
  Purchase #6 $49.72   13.396%   $56.3805   $56.38   $56.40   $56.40  
  Purchase #7 $188.43   13.202%   $213.3065   $213.31   $213.30   $213.30  
  7 purchase totals = $1,114.06       $1,234.2634   $1,234.25   $1,234.20   $1,234.30