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	$166.52	3.498%	$172.3449	$172.34	$172.35	$172.30
Purchase #2	$191.51	11.800%	$214.1082	$214.11	$214.10	$214.10
Purchase #3	$234.89	13.374%	$266.3042	$266.30	$266.30	$266.30
Purchase #4	$80.33	8.651%	$87.2793	$87.28	$87.30	$87.30
Purchase #5	$63.55	10.577%	$70.2717	$70.27	$70.25	$70.30
Purchase #6	$137.43	10.606%	$152.0058	$152.01	$152.00	$152.00
Purchase #7	$106.33	4.508%	$111.1234	$111.12	$111.10	$111.10
7 purchase totals =	$980.56		$1,073.4375	$1,073.43	$1,073.40	$1,073.40