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	$13.71	9.654%	$15.0336	$15.03	$15.05	$15.00
Purchase #2	$73.73	10.315%	$81.3352	$81.34	$81.35	$81.30
Purchase #3	$201.56	3.255%	$208.1208	$208.12	$208.10	$208.10
Purchase #4	$215.91	3.694%	$223.8857	$223.89	$223.90	$223.90
Purchase #5	$87.57	3.838%	$90.9309	$90.93	$90.95	$90.90
Purchase #6	$35.95	8.315%	$38.9392	$38.94	$38.95	$38.90
Purchase #7	$170.64	11.807%	$190.7875	$190.79	$190.80	$190.80
7 purchase totals =	$799.07		$849.0329	$849.04	$849.10	$848.90