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 $249.32   4.815%   $261.3248   $261.32   $261.30   $261.30  
  Purchase #2 $108.62   4.567%   $113.5807   $113.58   $113.60   $113.60  
  Purchase #3 $116.56   12.367%   $130.975   $130.98   $131.00   $131.00  
  Purchase #4 $129.75   3.535%   $134.3367   $134.34   $134.35   $134.30  
  Purchase #5 $241.68   9.322%   $264.2094   $264.21   $264.20   $264.20  
  Purchase #6 $194.73   12.577%   $219.2212   $219.22   $219.20   $219.20  
  Purchase #7 $18.99   13.492%   $21.5521   $21.55   $21.55   $21.60  
  7 purchase totals = $1,059.65       $1,145.1999   $1,145.20   $1,145.20   $1,145.20