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	$88.60	13.346%	$100.4246	$100.42	$100.40	$100.40
Purchase #2	$250.40	5.780%	$264.8731	$264.87	$264.85	$264.90
Purchase #3	$149.94	10.597%	$165.8291	$165.83	$165.85	$165.80
Purchase #4	$134.67	9.500%	$147.4637	$147.46	$147.45	$147.50
Purchase #5	$230.71	10.247%	$254.3509	$254.35	$254.35	$254.40
Purchase #6	$216.38	5.383%	$228.0277	$228.03	$228.05	$228.00
Purchase #7	$189.61	3.425%	$196.1041	$196.10	$196.10	$196.10
7 purchase totals =	$1,260.31		$1,357.0732	$1,357.06	$1,357.05	$1,357.10