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	$28.60	4.195%	$29.7998	$29.80	$29.80	$29.80
Purchase #2	$169.67	4.388%	$177.1151	$177.12	$177.10	$177.10
Purchase #3	$127.42	10.191%	$140.4054	$140.41	$140.40	$140.40
Purchase #4	$68.49	3.408%	$70.8241	$70.82	$70.80	$70.80
Purchase #5	$30.29	11.847%	$33.8785	$33.88	$33.90	$33.90
Purchase #6	$144.59	5.214%	$152.1289	$152.13	$152.15	$152.10
Purchase #7	$105.66	3.280%	$109.1256	$109.13	$109.15	$109.10
7 purchase totals =	$674.72		$713.2774	$713.29	$713.30	$713.20