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	$127.47	13.197%	$144.2922	$144.29	$144.30	$144.30
Purchase #2	$104.97	6.140%	$111.4152	$111.42	$111.40	$111.40
Purchase #3	$32.34	12.152%	$36.27	$36.27	$36.25	$36.30
Purchase #4	$55.30	5.274%	$58.2165	$58.22	$58.20	$58.20
Purchase #5	$181.85	12.844%	$205.2068	$205.21	$205.20	$205.20
Purchase #6	$156.40	6.344%	$166.322	$166.32	$166.30	$166.30
Purchase #7	$214.45	12.612%	$241.4964	$241.50	$241.50	$241.50
7 purchase totals =	$872.78		$963.2191	$963.23	$963.15	$963.20