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	$129.73	9.842%	$142.498	$142.50	$142.50	$142.50
Purchase #2	$223.27	12.363%	$250.8729	$250.87	$250.85	$250.90
Purchase #3	$149.70	10.735%	$165.7703	$165.77	$165.75	$165.80
Purchase #4	$154.87	12.269%	$173.871	$173.87	$173.85	$173.90
Purchase #5	$167.91	6.778%	$179.2909	$179.29	$179.30	$179.30
Purchase #6	$118.65	6.644%	$126.5331	$126.53	$126.55	$126.50
Purchase #7	$194.52	11.336%	$216.5708	$216.57	$216.55	$216.60
7 purchase totals =	$1,138.65		$1,255.4070	$1,255.40	$1,255.35	$1,255.50