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	$180.40	3.656%	$186.9954	$187.00	$187.00	$187.00
Purchase #2	$165.79	13.205%	$187.6826	$187.68	$187.70	$187.70
Purchase #3	$201.54	4.754%	$211.1212	$211.12	$211.10	$211.10
Purchase #4	$151.66	3.860%	$157.5141	$157.51	$157.50	$157.50
Purchase #5	$221.86	8.585%	$240.9067	$240.91	$240.90	$240.90
Purchase #6	$64.71	12.209%	$72.6104	$72.61	$72.60	$72.60
Purchase #7	$245.95	3.705%	$255.0624	$255.06	$255.05	$255.10
7 purchase totals =	$1,231.91		$1,311.8928	$1,311.89	$1,311.85	$1,311.90