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 $245.33   6.608%   $261.5414   $261.54   $261.55   $261.50  
  Purchase #2 $230.63   3.391%   $238.4507   $238.45   $238.45   $238.50  
  Purchase #3 $52.27   10.784%   $57.9068   $57.91   $57.90   $57.90  
  Purchase #4 $12.88   6.641%   $13.7354   $13.74   $13.75   $13.70  
  Purchase #5 $229.92   7.373%   $246.872   $246.87   $246.85   $246.90  
  Purchase #6 $117.87   5.510%   $124.3646   $124.36   $124.35   $124.40  
  Purchase #7 $22.65   12.293%   $25.4344   $25.43   $25.45   $25.40  
  7 purchase totals = $911.55       $968.3053   $968.30   $968.30   $968.30