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	$104.43	4.298%	$108.9184	$108.92	$108.90	$108.90
Purchase #2	$49.91	3.102%	$51.4582	$51.46	$51.45	$51.50
Purchase #3	$136.93	8.227%	$148.1952	$148.20	$148.20	$148.20
Purchase #4	$28.95	11.519%	$32.2848	$32.28	$32.30	$32.30
Purchase #5	$121.61	9.185%	$132.7799	$132.78	$132.80	$132.80
Purchase #6	$31.50	9.443%	$34.4745	$34.47	$34.45	$34.50
Purchase #7	$55.47	10.204%	$61.1302	$61.13	$61.15	$61.10
7 purchase totals =	$528.80		$569.2412	$569.24	$569.25	$569.30