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	$247.70	8.810%	$269.5224	$269.52	$269.50	$269.50
Purchase #2	$37.71	12.768%	$42.5248	$42.52	$42.50	$42.50
Purchase #3	$54.82	6.179%	$58.2073	$58.21	$58.20	$58.20
Purchase #4	$39.83	4.802%	$41.7426	$41.74	$41.75	$41.70
Purchase #5	$37.38	4.585%	$39.0939	$39.09	$39.10	$39.10
Purchase #6	$24.97	12.519%	$28.096	$28.10	$28.10	$28.10
Purchase #7	$111.48	9.846%	$122.4563	$122.46	$122.45	$122.50
7 purchase totals =	$553.89		$601.6433	$601.64	$601.60	$601.60