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 $231.92   6.468%   $246.9206   $246.92   $246.90   $246.90  
  Purchase #2 $161.39   13.232%   $182.7451   $182.75   $182.75   $182.70  
  Purchase #3 $107.32   4.472%   $112.1194   $112.12   $112.10   $112.10  
  Purchase #4 $210.72   6.639%   $224.7097   $224.71   $224.70   $224.70  
  Purchase #5 $156.89   6.713%   $167.422   $167.42   $167.40   $167.40  
  Purchase #6 $228.36   13.391%   $258.9397   $258.94   $258.95   $258.90  
  Purchase #7 $170.34   9.251%   $186.0982   $186.10   $186.10   $186.10  
  7 purchase totals = $1,266.94       $1,378.9547   $1,378.96   $1,378.90   $1,378.80