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	$21.84	6.205%	$23.1952	$23.20	$23.20	$23.20
Purchase #2	$176.57	11.222%	$196.3847	$196.38	$196.40	$196.40
Purchase #3	$107.97	8.258%	$116.8862	$116.89	$116.90	$116.90
Purchase #4	$20.75	4.162%	$21.6136	$21.61	$21.60	$21.60
Purchase #5	$167.84	6.554%	$178.8402	$178.84	$178.85	$178.80
Purchase #6	$160.62	5.503%	$169.4589	$169.46	$169.45	$169.50
Purchase #7	$148.57	11.181%	$165.1816	$165.18	$165.20	$165.20
7 purchase totals =	$804.16		$871.5604	$871.56	$871.60	$871.60