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	$170.62	4.508%	$178.3115	$178.31	$178.30	$178.30
Purchase #2	$227.67	10.283%	$251.0813	$251.08	$251.10	$251.10
Purchase #3	$185.49	5.779%	$196.2095	$196.21	$196.20	$196.20
Purchase #4	$64.86	9.824%	$71.2318	$71.23	$71.25	$71.20
Purchase #5	$214.87	6.794%	$229.4683	$229.47	$229.45	$229.50
Purchase #6	$38.92	8.604%	$42.2687	$42.27	$42.25	$42.30
Purchase #7	$28.84	3.495%	$29.848	$29.85	$29.85	$29.80
7 purchase totals =	$931.27		$998.4191	$998.42	$998.40	$998.40