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	$171.78	4.818%	$180.0564	$180.06	$180.05	$180.10
Purchase #2	$27.49	6.316%	$29.2263	$29.23	$29.25	$29.20
Purchase #3	$134.36	3.526%	$139.0975	$139.10	$139.10	$139.10
Purchase #4	$69.35	3.252%	$71.6053	$71.61	$71.60	$71.60
Purchase #5	$11.74	5.851%	$12.4269	$12.43	$12.45	$12.40
Purchase #6	$73.31	7.168%	$78.5649	$78.56	$78.55	$78.60
Purchase #7	$89.43	4.749%	$93.677	$93.68	$93.70	$93.70
7 purchase totals =	$577.46		$604.6543	$604.67	$604.70	$604.70