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	$94.90	3.777%	$98.4844	$98.48	$98.50	$98.50
Purchase #2	$146.91	7.485%	$157.9062	$157.91	$157.90	$157.90
Purchase #3	$99.62	10.337%	$109.9177	$109.92	$109.90	$109.90
Purchase #4	$131.27	9.627%	$143.9074	$143.91	$143.90	$143.90
Purchase #5	$122.69	3.398%	$126.859	$126.86	$126.85	$126.90
Purchase #6	$214.69	11.806%	$240.0363	$240.04	$240.05	$240.00
Purchase #7	$16.78	8.604%	$18.2238	$18.22	$18.20	$18.20
7 purchase totals =	$826.86		$895.3348	$895.34	$895.30	$895.30