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 $26.38   13.546%   $29.9534   $29.95   $29.95   $30.00  
  Purchase #2 $207.88   3.257%   $214.6507   $214.65   $214.65   $214.70  
  Purchase #3 $193.88   4.126%   $201.8795   $201.88   $201.90   $201.90  
  Purchase #4 $28.47   13.658%   $32.3584   $32.36   $32.35   $32.40  
  Purchase #5 $238.86   3.197%   $246.4964   $246.50   $246.50   $246.50  
  Purchase #6 $244.26   11.447%   $272.2204   $272.22   $272.20   $272.20  
  Purchase #7 $234.37   11.609%   $261.578   $261.58   $261.60   $261.60  
  7 purchase totals = $1,174.10       $1,259.1368   $1,259.14   $1,259.15   $1,259.30