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	$142.26	4.638%	$148.858	$148.86	$148.85	$148.90
Purchase #2	$92.62	4.201%	$96.511	$96.51	$96.50	$96.50
Purchase #3	$70.30	10.799%	$77.8917	$77.89	$77.90	$77.90
Purchase #4	$12.63	7.200%	$13.5394	$13.54	$13.55	$13.50
Purchase #5	$133.72	7.149%	$143.2796	$143.28	$143.30	$143.30
Purchase #6	$19.65	7.665%	$21.1562	$21.16	$21.15	$21.20
Purchase #7	$151.65	8.851%	$165.0725	$165.07	$165.05	$165.10
7 purchase totals =	$622.83		$666.3084	$666.31	$666.30	$666.40