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 $56.59   11.820%   $63.2789   $63.28   $63.30   $63.30  
  Purchase #2 $162.79   8.859%   $177.2116   $177.21   $177.20   $177.20  
  Purchase #3 $32.67   5.515%   $34.4718   $34.47   $34.45   $34.50  
  Purchase #4 $230.87   13.201%   $261.3471   $261.35   $261.35   $261.30  
  Purchase #5 $227.90   8.747%   $247.8344   $247.83   $247.85   $247.80  
  Purchase #6 $170.95   13.250%   $193.6009   $193.60   $193.60   $193.60  
  Purchase #7 $249.65   7.432%   $268.204   $268.20   $268.20   $268.20  
  7 purchase totals = $1,131.42       $1,245.9487   $1,245.94   $1,245.95   $1,245.90