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	$237.34	12.278%	$266.4806	$266.48	$266.50	$266.50
Purchase #2	$79.90	13.367%	$90.5802	$90.58	$90.60	$90.60
Purchase #3	$156.42	12.114%	$175.3687	$175.37	$175.35	$175.40
Purchase #4	$250.89	12.132%	$281.328	$281.33	$281.35	$281.30
Purchase #5	$134.71	3.645%	$139.6202	$139.62	$139.60	$139.60
Purchase #6	$206.44	8.273%	$223.5188	$223.52	$223.50	$223.50
Purchase #7	$204.41	11.733%	$228.3934	$228.39	$228.40	$228.40
7 purchase totals =	$1,270.11		$1,405.2899	$1,405.29	$1,405.30	$1,405.30