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 $46.41   11.494%   $51.7444   $51.74   $51.75   $51.70  
  Purchase #2 $131.38   11.200%   $146.0946   $146.09   $146.10   $146.10  
  Purchase #3 $246.86   4.800%   $258.7093   $258.71   $258.70   $258.70  
  Purchase #4 $167.42   12.385%   $188.155   $188.16   $188.15   $188.20  
  Purchase #5 $171.94   4.173%   $179.1151   $179.12   $179.10   $179.10  
  Purchase #6 $190.50   12.722%   $214.7354   $214.74   $214.75   $214.70  
  Purchase #7 $202.41   5.841%   $214.2328   $214.23   $214.25   $214.20  
  7 purchase totals = $1,156.92       $1,252.7866   $1,252.79   $1,252.80   $1,252.70