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 $29.27   11.272%   $32.5693   $32.57   $32.55   $32.60  
  Purchase #2 $216.99   13.339%   $245.9343   $245.93   $245.95   $245.90  
  Purchase #3 $78.97   3.309%   $81.5831   $81.58   $81.60   $81.60  
  Purchase #4 $45.53   8.757%   $49.5171   $49.52   $49.50   $49.50  
  Purchase #5 $231.51   12.872%   $261.31   $261.31   $261.30   $261.30  
  Purchase #6 $170.57   4.126%   $177.6077   $177.61   $177.60   $177.60  
  Purchase #7 $51.43   6.208%   $54.6228   $54.62   $54.60   $54.60  
  7 purchase totals = $824.27       $903.1443   $903.14   $903.10   $903.10