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	$91.72	9.766%	$100.6774	$100.68	$100.70	$100.70
Purchase #2	$158.88	8.377%	$172.1894	$172.19	$172.20	$172.20
Purchase #3	$29.33	11.812%	$32.7945	$32.79	$32.80	$32.80
Purchase #4	$124.43	11.181%	$138.3425	$138.34	$138.35	$138.30
Purchase #5	$42.72	8.484%	$46.3444	$46.34	$46.35	$46.30
Purchase #6	$96.63	3.555%	$100.0652	$100.07	$100.05	$100.10
Purchase #7	$9.80	4.150%	$10.2067	$10.21	$10.20	$10.20
7 purchase totals =	$553.51		$600.6201	$600.62	$600.65	$600.60