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	$78.49	6.847%	$83.8642	$83.86	$83.85	$83.90
Purchase #2	$17.43	6.244%	$18.5183	$18.52	$18.50	$18.50
Purchase #3	$142.32	8.102%	$153.8508	$153.85	$153.85	$153.90
Purchase #4	$90.85	13.476%	$103.0929	$103.09	$103.10	$103.10
Purchase #5	$110.31	9.392%	$120.6703	$120.67	$120.65	$120.70
Purchase #6	$89.71	5.453%	$94.6019	$94.60	$94.60	$94.60
Purchase #7	$69.83	5.717%	$73.8222	$73.82	$73.80	$73.80
7 purchase totals =	$598.94		$648.4206	$648.41	$648.35	$648.50