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	$136.49	3.785%	$141.6561	$141.66	$141.65	$141.70
Purchase #2	$156.42	9.714%	$171.6146	$171.61	$171.60	$171.60
Purchase #3	$228.51	4.377%	$238.5119	$238.51	$238.50	$238.50
Purchase #4	$163.76	5.199%	$172.2739	$172.27	$172.25	$172.30
Purchase #5	$228.67	7.521%	$245.8683	$245.87	$245.85	$245.90
Purchase #6	$123.35	4.112%	$128.4222	$128.42	$128.40	$128.40
Purchase #7	$228.91	4.761%	$239.8084	$239.81	$239.80	$239.80
7 purchase totals =	$1,266.11		$1,338.1554	$1,338.15	$1,338.05	$1,338.20