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	$136.58	11.732%	$152.6036	$152.60	$152.60	$152.60
Purchase #2	$31.39	13.175%	$35.5256	$35.53	$35.55	$35.50
Purchase #3	$190.81	10.265%	$210.3966	$210.40	$210.40	$210.40
Purchase #4	$59.64	3.569%	$61.7686	$61.77	$61.75	$61.80
Purchase #5	$183.89	4.130%	$191.4847	$191.48	$191.50	$191.50
Purchase #6	$199.39	5.143%	$209.6446	$209.64	$209.65	$209.60
Purchase #7	$204.43	12.537%	$230.0594	$230.06	$230.05	$230.10
7 purchase totals =	$1,006.13		$1,091.4831	$1,091.48	$1,091.50	$1,091.50