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	$17.71	6.344%	$18.8335	$18.83	$18.85	$18.80
Purchase #2	$201.94	13.118%	$228.4305	$228.43	$228.45	$228.40
Purchase #3	$150.91	11.182%	$167.7848	$167.78	$167.80	$167.80
Purchase #4	$166.29	13.734%	$189.1283	$189.13	$189.15	$189.10
Purchase #5	$167.41	7.403%	$179.8034	$179.80	$179.80	$179.80
Purchase #6	$225.39	12.378%	$253.2888	$253.29	$253.30	$253.30
Purchase #7	$56.55	5.699%	$59.7728	$59.77	$59.75	$59.80
7 purchase totals =	$986.20		$1,097.0421	$1,097.03	$1,097.10	$1,097.00