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	$40.94	3.662%	$42.4392	$42.44	$42.45	$42.40
Purchase #2	$115.76	6.259%	$123.0054	$123.01	$123.00	$123.00
Purchase #3	$110.74	4.854%	$116.1153	$116.12	$116.10	$116.10
Purchase #4	$96.97	10.644%	$107.2915	$107.29	$107.30	$107.30
Purchase #5	$146.72	3.537%	$151.9095	$151.91	$151.90	$151.90
Purchase #6	$130.75	6.628%	$139.4161	$139.42	$139.40	$139.40
Purchase #7	$116.90	5.169%	$122.9426	$122.94	$122.95	$122.90
7 purchase totals =	$758.78		$803.1196	$803.13	$803.10	$803.00