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	$30.78	4.821%	$32.2639	$32.26	$32.25	$32.30
Purchase #2	$89.59	11.185%	$99.6106	$99.61	$99.60	$99.60
Purchase #3	$99.90	4.543%	$104.4385	$104.44	$104.45	$104.40
Purchase #4	$65.94	6.179%	$70.0144	$70.01	$70.00	$70.00
Purchase #5	$148.75	3.292%	$153.6469	$153.65	$153.65	$153.60
Purchase #6	$114.89	4.786%	$120.3886	$120.39	$120.40	$120.40
Purchase #7	$125.51	10.535%	$138.7325	$138.73	$138.75	$138.70
7 purchase totals =	$675.36		$719.0954	$719.09	$719.10	$719.00