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	$162.37	6.662%	$173.1871	$173.19	$173.20	$173.20
Purchase #2	$42.48	13.455%	$48.1957	$48.20	$48.20	$48.20
Purchase #3	$141.81	12.343%	$159.3136	$159.31	$159.30	$159.30
Purchase #4	$137.38	4.826%	$144.01	$144.01	$144.00	$144.00
Purchase #5	$100.52	10.507%	$111.0816	$111.08	$111.10	$111.10
Purchase #6	$73.48	12.538%	$82.6929	$82.69	$82.70	$82.70
Purchase #7	$100.55	10.205%	$110.8111	$110.81	$110.80	$110.80
7 purchase totals =	$758.59		$829.2920	$829.29	$829.30	$829.30