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	$18.45	11.408%	$20.5548	$20.55	$20.55	$20.60
Purchase #2	$221.70	4.495%	$231.6654	$231.67	$231.65	$231.70
Purchase #3	$167.33	10.241%	$184.4663	$184.47	$184.45	$184.50
Purchase #4	$72.71	13.391%	$82.4466	$82.45	$82.45	$82.40
Purchase #5	$49.29	7.594%	$53.0331	$53.03	$53.05	$53.00
Purchase #6	$206.81	4.113%	$215.3161	$215.32	$215.30	$215.30
Purchase #7	$158.90	12.813%	$179.2599	$179.26	$179.25	$179.30
7 purchase totals =	$895.19		$966.7422	$966.75	$966.70	$966.80