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	$223.78	5.788%	$236.7324	$236.73	$236.75	$236.70
Purchase #2	$110.37	9.113%	$120.428	$120.43	$120.45	$120.40
Purchase #3	$49.35	6.496%	$52.5558	$52.56	$52.55	$52.60
Purchase #4	$97.84	13.783%	$111.3253	$111.33	$111.35	$111.30
Purchase #5	$135.93	5.634%	$143.5883	$143.59	$143.60	$143.60
Purchase #6	$46.88	3.855%	$48.6872	$48.69	$48.70	$48.70
Purchase #7	$27.74	12.117%	$31.1013	$31.10	$31.10	$31.10
7 purchase totals =	$691.89		$744.4183	$744.43	$744.50	$744.40