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	$153.63	3.485%	$158.984	$158.98	$159.00	$159.00
Purchase #2	$173.96	6.501%	$185.2691	$185.27	$185.25	$185.30
Purchase #3	$131.93	13.701%	$150.0057	$150.01	$150.00	$150.00
Purchase #4	$137.26	3.251%	$141.7223	$141.72	$141.70	$141.70
Purchase #5	$128.45	3.162%	$132.5116	$132.51	$132.50	$132.50
Purchase #6	$223.53	6.377%	$237.7845	$237.78	$237.80	$237.80
Purchase #7	$123.42	6.483%	$131.4213	$131.42	$131.40	$131.40
7 purchase totals =	$1,072.18		$1,137.6985	$1,137.69	$1,137.65	$1,137.70