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	$177.82	12.578%	$200.1862	$200.19	$200.20	$200.20
Purchase #2	$56.50	5.411%	$59.5572	$59.56	$59.55	$59.60
Purchase #3	$158.30	4.636%	$165.6388	$165.64	$165.65	$165.60
Purchase #4	$59.53	11.757%	$66.5289	$66.53	$66.55	$66.50
Purchase #5	$94.93	5.858%	$100.491	$100.49	$100.50	$100.50
Purchase #6	$76.61	9.399%	$83.8106	$83.81	$83.80	$83.80
Purchase #7	$82.26	7.177%	$88.1638	$88.16	$88.15	$88.20
7 purchase totals =	$705.95		$764.3765	$764.38	$764.40	$764.40