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	$247.97	10.637%	$274.3466	$274.35	$274.35	$274.30
Purchase #2	$159.84	13.773%	$181.8548	$181.85	$181.85	$181.90
Purchase #3	$70.25	13.160%	$79.4949	$79.49	$79.50	$79.50
Purchase #4	$94.90	10.598%	$104.9575	$104.96	$104.95	$105.00
Purchase #5	$246.27	12.120%	$276.1179	$276.12	$276.10	$276.10
Purchase #6	$97.65	8.158%	$105.6163	$105.62	$105.60	$105.60
Purchase #7	$229.94	10.251%	$253.5111	$253.51	$253.50	$253.50
7 purchase totals =	$1,146.82		$1,275.8991	$1,275.90	$1,275.85	$1,275.90