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 $61.96   3.803%   $64.3163   $64.32   $64.30   $64.30  
  Purchase #2 $186.72   5.671%   $197.3089   $197.31   $197.30   $197.30  
  Purchase #3 $239.27   6.598%   $255.057   $255.06   $255.05   $255.10  
  Purchase #4 $228.68   9.625%   $250.6905   $250.69   $250.70   $250.70  
  Purchase #5 $120.26   11.199%   $133.7279   $133.73   $133.75   $133.70  
  Purchase #6 $242.63   10.872%   $269.0087   $269.01   $269.00   $269.00  
  Purchase #7 $206.86   12.784%   $233.305   $233.31   $233.30   $233.30  
  7 purchase totals = $1,286.38       $1,403.4143   $1,403.43   $1,403.40   $1,403.40