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	$232.96	8.720%	$253.2741	$253.27	$253.25	$253.30
Purchase #2	$81.71	9.673%	$89.6138	$89.61	$89.60	$89.60
Purchase #3	$223.35	13.667%	$253.8752	$253.88	$253.90	$253.90
Purchase #4	$48.49	10.192%	$53.4321	$53.43	$53.45	$53.40
Purchase #5	$46.86	9.670%	$51.3914	$51.39	$51.40	$51.40
Purchase #6	$247.69	3.591%	$256.5845	$256.58	$256.60	$256.60
Purchase #7	$140.91	12.399%	$158.3814	$158.38	$158.40	$158.40
7 purchase totals =	$1,021.97		$1,116.5525	$1,116.54	$1,116.60	$1,116.60