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	$18.41	10.835%	$20.4047	$20.40	$20.40	$20.40
Purchase #2	$152.95	12.791%	$172.5138	$172.51	$172.50	$172.50
Purchase #3	$56.41	5.589%	$59.5628	$59.56	$59.55	$59.60
Purchase #4	$40.80	4.729%	$42.7294	$42.73	$42.75	$42.70
Purchase #5	$6.93	10.635%	$7.667	$7.67	$7.65	$7.70
Purchase #6	$233.68	3.412%	$241.6532	$241.65	$241.65	$241.70
Purchase #7	$85.99	7.634%	$92.5545	$92.55	$92.55	$92.60
7 purchase totals =	$595.17		$637.0854	$637.07	$637.05	$637.20