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	$170.85	4.520%	$178.5724	$178.57	$178.55	$178.60
Purchase #2	$166.77	7.201%	$178.7791	$178.78	$178.80	$178.80
Purchase #3	$84.89	4.348%	$88.581	$88.58	$88.60	$88.60
Purchase #4	$113.64	12.264%	$127.5768	$127.58	$127.60	$127.60
Purchase #5	$129.41	13.516%	$146.9011	$146.90	$146.90	$146.90
Purchase #6	$107.86	3.254%	$111.3698	$111.37	$111.35	$111.40
Purchase #7	$127.56	10.450%	$140.89	$140.89	$140.90	$140.90
7 purchase totals =	$900.98		$972.6702	$972.67	$972.70	$972.80