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	$149.29	4.813%	$156.4753	$156.48	$156.50	$156.50
Purchase #2	$160.96	8.631%	$174.8525	$174.85	$174.85	$174.90
Purchase #3	$79.72	11.688%	$89.0377	$89.04	$89.05	$89.00
Purchase #4	$239.47	10.268%	$264.0588	$264.06	$264.05	$264.10
Purchase #5	$241.35	8.609%	$262.1278	$262.13	$262.15	$262.10
Purchase #6	$104.94	11.834%	$117.3586	$117.36	$117.35	$117.40
Purchase #7	$44.49	3.196%	$45.9119	$45.91	$45.90	$45.90
7 purchase totals =	$1,020.22		$1,109.8226	$1,109.83	$1,109.85	$1,109.90