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	$55.90	5.594%	$59.027	$59.03	$59.05	$59.00
Purchase #2	$21.94	4.471%	$22.9209	$22.92	$22.90	$22.90
Purchase #3	$66.32	5.707%	$70.1049	$70.10	$70.10	$70.10
Purchase #4	$85.78	5.306%	$90.3315	$90.33	$90.35	$90.30
Purchase #5	$68.62	6.741%	$73.2457	$73.25	$73.25	$73.20
Purchase #6	$240.91	3.229%	$248.689	$248.69	$248.70	$248.70
Purchase #7	$91.49	8.631%	$99.3865	$99.39	$99.40	$99.40
7 purchase totals =	$630.96		$663.7055	$663.71	$663.75	$663.60