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	$81.93	10.456%	$90.4966	$90.50	$90.50	$90.50
Purchase #2	$72.65	8.408%	$78.7584	$78.76	$78.75	$78.80
Purchase #3	$221.42	11.236%	$246.2988	$246.30	$246.30	$246.30
Purchase #4	$229.49	6.546%	$244.5124	$244.51	$244.50	$244.50
Purchase #5	$148.69	6.552%	$158.4322	$158.43	$158.45	$158.40
Purchase #6	$93.92	4.230%	$97.8928	$97.89	$97.90	$97.90
Purchase #7	$77.91	12.196%	$87.4119	$87.41	$87.40	$87.40
7 purchase totals =	$926.01		$1,003.8031	$1,003.80	$1,003.80	$1,003.80