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 $64.74   5.255%   $68.1421   $68.14   $68.15   $68.10  
  Purchase #2 $27.62   9.316%   $30.1931   $30.19   $30.20   $30.20  
  Purchase #3 $238.63   10.196%   $262.9607   $262.96   $262.95   $263.00  
  Purchase #4 $71.46   5.784%   $75.5932   $75.59   $75.60   $75.60  
  Purchase #5 $170.34   4.128%   $177.3716   $177.37   $177.35   $177.40  
  Purchase #6 $181.71   13.601%   $206.4244   $206.42   $206.40   $206.40  
  Purchase #7 $234.76   8.595%   $254.9376   $254.94   $254.95   $254.90  
  7 purchase totals = $989.26       $1,075.6227   $1,075.61   $1,075.60   $1,075.60