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	$153.58	7.817%	$165.5853	$165.59	$165.60	$165.60
Purchase #2	$157.42	10.465%	$173.894	$173.89	$173.90	$173.90
Purchase #3	$170.78	4.238%	$178.0177	$178.02	$178.00	$178.00
Purchase #4	$91.30	3.841%	$94.8068	$94.81	$94.80	$94.80
Purchase #5	$109.51	13.726%	$124.5413	$124.54	$124.55	$124.50
Purchase #6	$75.77	10.767%	$83.9282	$83.93	$83.95	$83.90
Purchase #7	$54.58	9.172%	$59.5861	$59.59	$59.60	$59.60
7 purchase totals =	$812.94		$880.3594	$880.37	$880.40	$880.30