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	$154.93	6.213%	$164.5558	$164.56	$164.55	$164.60
Purchase #2	$46.76	3.663%	$48.4728	$48.47	$48.45	$48.50
Purchase #3	$49.58	11.435%	$55.2495	$55.25	$55.25	$55.20
Purchase #4	$245.47	5.570%	$259.1427	$259.14	$259.15	$259.10
Purchase #5	$16.34	6.819%	$17.4542	$17.45	$17.45	$17.50
Purchase #6	$118.48	4.502%	$123.814	$123.81	$123.80	$123.80
Purchase #7	$223.45	8.515%	$242.4768	$242.48	$242.50	$242.50
7 purchase totals =	$855.01		$911.1658	$911.16	$911.15	$911.20