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 $115.71   6.313%   $123.0148   $123.01   $123.00   $123.00  
  Purchase #2 $210.30   11.246%   $233.9503   $233.95   $233.95   $234.00  
  Purchase #3 $190.66   5.281%   $200.7288   $200.73   $200.75   $200.70  
  Purchase #4 $60.91   4.177%   $63.4542   $63.45   $63.45   $63.50  
  Purchase #5 $57.84   12.426%   $65.0272   $65.03   $65.05   $65.00  
  Purchase #6 $57.25   13.360%   $64.8986   $64.90   $64.90   $64.90  
  Purchase #7 $15.66   4.467%   $16.3595   $16.36   $16.35   $16.40  
  7 purchase totals = $708.33       $767.4334   $767.43   $767.45   $767.50