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	$16.37	13.656%	$18.6055	$18.61	$18.60	$18.60
Purchase #2	$188.89	12.460%	$212.4257	$212.43	$212.45	$212.40
Purchase #3	$97.78	11.358%	$108.8859	$108.89	$108.90	$108.90
Purchase #4	$41.66	12.146%	$46.72	$46.72	$46.70	$46.70
Purchase #5	$238.89	4.573%	$249.8144	$249.81	$249.80	$249.80
Purchase #6	$165.85	10.793%	$183.7502	$183.75	$183.75	$183.80
Purchase #7	$234.31	4.425%	$244.6782	$244.68	$244.70	$244.70
7 purchase totals =	$983.75		$1,064.8799	$1,064.89	$1,064.90	$1,064.90