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	$95.74	10.498%	$105.7908	$105.79	$105.80	$105.80
Purchase #2	$79.73	4.228%	$83.101	$83.10	$83.10	$83.10
Purchase #3	$31.73	6.236%	$33.7087	$33.71	$33.70	$33.70
Purchase #4	$229.45	11.188%	$255.1209	$255.12	$255.10	$255.10
Purchase #5	$93.52	12.310%	$105.0323	$105.03	$105.05	$105.00
Purchase #6	$20.28	4.230%	$21.1378	$21.14	$21.15	$21.10
Purchase #7	$34.30	7.315%	$36.809	$36.81	$36.80	$36.80
7 purchase totals =	$584.75		$640.7005	$640.70	$640.70	$640.60