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	$250.48	12.519%	$281.8376	$281.84	$281.85	$281.80
Purchase #2	$69.28	3.130%	$71.4485	$71.45	$71.45	$71.40
Purchase #3	$198.86	6.302%	$211.3922	$211.39	$211.40	$211.40
Purchase #4	$62.27	13.863%	$70.9025	$70.90	$70.90	$70.90
Purchase #5	$132.31	5.556%	$139.6611	$139.66	$139.65	$139.70
Purchase #6	$250.59	10.608%	$277.1726	$277.17	$277.15	$277.20
Purchase #7	$114.32	4.221%	$119.1454	$119.15	$119.15	$119.10
7 purchase totals =	$1,078.11		$1,171.5599	$1,171.56	$1,171.55	$1,171.50