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 $247.57   5.819%   $261.9761   $261.98   $262.00   $262.00  
  Purchase #2 $131.60   4.667%   $137.7418   $137.74   $137.75   $137.70  
  Purchase #3 $14.90   11.590%   $16.6269   $16.63   $16.65   $16.60  
  Purchase #4 $103.64   7.677%   $111.5964   $111.60   $111.60   $111.60  
  Purchase #5 $207.45   3.553%   $214.8207   $214.82   $214.80   $214.80  
  Purchase #6 $49.26   11.298%   $54.8254   $54.83   $54.85   $54.80  
  Purchase #7 $14.37   13.569%   $16.3199   $16.32   $16.30   $16.30  
  7 purchase totals = $768.79       $813.9072   $813.92   $813.95   $813.80