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 $244.77   7.431%   $262.9589   $262.96   $262.95   $263.00  
  Purchase #2 $21.38   9.786%   $23.4722   $23.47   $23.45   $23.50  
  Purchase #3 $28.79   3.223%   $29.7179   $29.72   $29.70   $29.70  
  Purchase #4 $67.60   4.498%   $70.6406   $70.64   $70.65   $70.60  
  Purchase #5 $179.62   9.307%   $196.3372   $196.34   $196.35   $196.30  
  Purchase #6 $115.88   5.473%   $122.2221   $122.22   $122.20   $122.20  
  Purchase #7 $40.91   12.386%   $45.9771   $45.98   $46.00   $46.00  
  7 purchase totals = $698.95       $751.3260   $751.33   $751.30   $751.30