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	$16.89	6.119%	$17.9235	$17.92	$17.90	$17.90
Purchase #2	$127.72	10.776%	$141.4831	$141.48	$141.50	$141.50
Purchase #3	$29.29	6.502%	$31.1944	$31.19	$31.20	$31.20
Purchase #4	$196.42	13.229%	$222.4044	$222.40	$222.40	$222.40
Purchase #5	$49.91	7.216%	$53.5115	$53.51	$53.50	$53.50
Purchase #6	$27.61	9.579%	$30.2548	$30.25	$30.25	$30.30
Purchase #7	$145.29	3.147%	$149.8623	$149.86	$149.85	$149.90
7 purchase totals =	$593.13		$646.6340	$646.61	$646.60	$646.70