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	$40.52	11.377%	$45.13	$45.13	$45.15	$45.10
Purchase #2	$107.65	13.637%	$122.3302	$122.33	$122.35	$122.30
Purchase #3	$148.95	4.322%	$155.3876	$155.39	$155.40	$155.40
Purchase #4	$71.73	8.503%	$77.8292	$77.83	$77.85	$77.80
Purchase #5	$109.56	8.167%	$118.5078	$118.51	$118.50	$118.50
Purchase #6	$110.48	8.186%	$119.5239	$119.52	$119.50	$119.50
Purchase #7	$180.86	5.784%	$191.3209	$191.32	$191.30	$191.30
7 purchase totals =	$769.75		$830.0296	$830.03	$830.05	$829.90