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	$242.26	12.185%	$271.7794	$271.78	$271.80	$271.80
Purchase #2	$14.52	4.379%	$15.1558	$15.16	$15.15	$15.20
Purchase #3	$79.29	13.511%	$90.0029	$90.00	$90.00	$90.00
Purchase #4	$80.84	6.316%	$85.9459	$85.95	$85.95	$85.90
Purchase #5	$93.48	6.575%	$99.6263	$99.63	$99.65	$99.60
Purchase #6	$21.38	3.132%	$22.0496	$22.05	$22.05	$22.00
Purchase #7	$56.93	7.267%	$61.0671	$61.07	$61.05	$61.10
7 purchase totals =	$588.70		$645.6270	$645.64	$645.65	$645.60