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	$110.37	3.212%	$113.9151	$113.92	$113.90	$113.90
Purchase #2	$47.81	6.433%	$50.8856	$50.89	$50.90	$50.90
Purchase #3	$20.56	3.843%	$21.3501	$21.35	$21.35	$21.40
Purchase #4	$37.77	12.818%	$42.6114	$42.61	$42.60	$42.60
Purchase #5	$106.65	11.310%	$118.7121	$118.71	$118.70	$118.70
Purchase #6	$49.64	8.181%	$53.701	$53.70	$53.70	$53.70
Purchase #7	$168.41	6.239%	$178.9171	$178.92	$178.90	$178.90
7 purchase totals =	$541.21		$580.0924	$580.10	$580.05	$580.10