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 $235.37   4.770%   $246.5971   $246.60   $246.60   $246.60  
  Purchase #2 $27.47   8.510%   $29.8077   $29.81   $29.80   $29.80  
  Purchase #3 $16.71   10.548%   $18.4726   $18.47   $18.45   $18.50  
  Purchase #4 $246.92   5.254%   $259.8932   $259.89   $259.90   $259.90  
  Purchase #5 $145.25   6.201%   $154.257   $154.26   $154.25   $154.30  
  Purchase #6 $56.85   9.590%   $62.3019   $62.30   $62.30   $62.30  
  Purchase #7 $22.55   7.856%   $24.3215   $24.32   $24.30   $24.30  
  7 purchase totals = $751.12       $795.6510   $795.65   $795.60   $795.70