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	$128.56	3.627%	$133.2229	$133.22	$133.20	$133.20
Purchase #2	$138.48	11.108%	$153.8624	$153.86	$153.85	$153.90
Purchase #3	$171.56	7.821%	$184.9777	$184.98	$185.00	$185.00
Purchase #4	$30.89	4.809%	$32.3755	$32.38	$32.40	$32.40
Purchase #5	$166.34	11.142%	$184.8736	$184.87	$184.85	$184.90
Purchase #6	$104.52	6.374%	$111.1821	$111.18	$111.20	$111.20
Purchase #7	$15.46	11.784%	$17.2818	$17.28	$17.30	$17.30
7 purchase totals =	$755.81		$817.7760	$817.77	$817.80	$817.90