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 $46.33   6.567%   $49.3725   $49.37   $49.35   $49.40  
  Purchase #2 $115.75   6.776%   $123.5932   $123.59   $123.60   $123.60  
  Purchase #3 $192.27   4.504%   $200.9298   $200.93   $200.95   $200.90  
  Purchase #4 $226.84   5.144%   $238.5086   $238.51   $238.50   $238.50  
  Purchase #5 $170.45   8.532%   $184.9928   $184.99   $185.00   $185.00  
  Purchase #6 $119.54   11.664%   $133.4831   $133.48   $133.50   $133.50  
  Purchase #7 $193.49   12.466%   $217.6105   $217.61   $217.60   $217.60  
  7 purchase totals = $1,064.67       $1,148.4905   $1,148.48   $1,148.50   $1,148.50