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 $57.86   12.247%   $64.9461   $64.95   $64.95   $64.90  
  Purchase #2 $117.73   10.589%   $130.1964   $130.20   $130.20   $130.20  
  Purchase #3 $136.53   12.692%   $153.8584   $153.86   $153.85   $153.90  
  Purchase #4 $164.50   7.397%   $176.6681   $176.67   $176.65   $176.70  
  Purchase #5 $183.46   10.461%   $202.6518   $202.65   $202.65   $202.70  
  Purchase #6 $249.48   6.149%   $264.8205   $264.82   $264.80   $264.80  
  Purchase #7 $70.31   4.619%   $73.5576   $73.56   $73.55   $73.60  
  7 purchase totals = $979.87       $1,066.6989   $1,066.71   $1,066.65   $1,066.80