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 $32.51   6.542%   $34.6368   $34.64   $34.65   $34.60  
  Purchase #2 $55.79   4.263%   $58.1683   $58.17   $58.15   $58.20  
  Purchase #3 $70.45   8.647%   $76.5418   $76.54   $76.55   $76.50  
  Purchase #4 $40.47   11.784%   $45.239   $45.24   $45.25   $45.20  
  Purchase #5 $146.58   4.702%   $153.4722   $153.47   $153.45   $153.50  
  Purchase #6 $126.44   8.305%   $136.9408   $136.94   $136.95   $136.90  
  Purchase #7 $231.98   12.546%   $261.0842   $261.08   $261.10   $261.10  
  7 purchase totals = $704.22       $766.0831   $766.08   $766.10   $766.00