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	$11.64	13.104%	$13.1653	$13.17	$13.15	$13.20
Purchase #2	$52.91	6.544%	$56.3724	$56.37	$56.35	$56.40
Purchase #3	$45.89	5.710%	$48.5103	$48.51	$48.50	$48.50
Purchase #4	$55.77	7.150%	$59.7576	$59.76	$59.75	$59.80
Purchase #5	$55.78	5.130%	$58.6415	$58.64	$58.65	$58.60
Purchase #6	$37.40	10.479%	$41.3191	$41.32	$41.30	$41.30
Purchase #7	$138.60	13.700%	$157.5882	$157.59	$157.60	$157.60
7 purchase totals =	$397.99		$435.3544	$435.36	$435.30	$435.40