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	$5.99	11.650%	$6.6878	$6.69	$6.70	$6.70
Purchase #2	$71.73	9.759%	$78.7301	$78.73	$78.75	$78.70
Purchase #3	$242.81	5.790%	$256.8687	$256.87	$256.85	$256.90
Purchase #4	$168.43	13.856%	$191.7677	$191.77	$191.75	$191.80
Purchase #5	$209.39	13.772%	$238.2272	$238.23	$238.25	$238.20
Purchase #6	$84.63	4.572%	$88.4993	$88.50	$88.50	$88.50
Purchase #7	$247.65	3.329%	$255.8943	$255.89	$255.90	$255.90
7 purchase totals =	$1,030.63		$1,116.6751	$1,116.68	$1,116.70	$1,116.70