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	$84.42	7.613%	$90.8469	$90.85	$90.85	$90.80
Purchase #2	$209.95	7.362%	$225.4065	$225.41	$225.40	$225.40
Purchase #3	$220.89	13.146%	$249.9282	$249.93	$249.95	$249.90
Purchase #4	$228.79	6.793%	$244.3317	$244.33	$244.35	$244.30
Purchase #5	$128.64	12.151%	$144.271	$144.27	$144.25	$144.30
Purchase #6	$235.87	8.389%	$255.6571	$255.66	$255.65	$255.70
Purchase #7	$124.95	11.581%	$139.4205	$139.42	$139.40	$139.40
7 purchase totals =	$1,233.51		$1,349.8619	$1,349.87	$1,349.85	$1,349.80