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	$85.52	7.217%	$91.692	$91.69	$91.70	$91.70
Purchase #2	$243.25	4.410%	$253.9773	$253.98	$254.00	$254.00
Purchase #3	$131.69	11.501%	$146.8357	$146.84	$146.85	$146.80
Purchase #4	$168.40	6.574%	$179.4706	$179.47	$179.45	$179.50
Purchase #5	$117.30	5.208%	$123.409	$123.41	$123.40	$123.40
Purchase #6	$71.73	7.664%	$77.2274	$77.23	$77.25	$77.20
Purchase #7	$81.62	6.808%	$87.1767	$87.18	$87.20	$87.20
7 purchase totals =	$899.51		$959.7887	$959.80	$959.85	$959.80