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	$236.89	4.106%	$246.6167	$246.62	$246.60	$246.60
Purchase #2	$135.58	6.691%	$144.6517	$144.65	$144.65	$144.70
Purchase #3	$147.64	6.417%	$157.1141	$157.11	$157.10	$157.10
Purchase #4	$37.61	13.550%	$42.7062	$42.71	$42.70	$42.70
Purchase #5	$102.39	6.705%	$109.2552	$109.26	$109.25	$109.30
Purchase #6	$223.29	3.653%	$231.4468	$231.45	$231.45	$231.40
Purchase #7	$158.70	8.542%	$172.2562	$172.26	$172.25	$172.30
7 purchase totals =	$1,042.10		$1,104.0469	$1,104.06	$1,104.00	$1,104.10