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	$172.31	10.556%	$190.499	$190.50	$190.50	$190.50
Purchase #2	$101.71	7.328%	$109.1633	$109.16	$109.15	$109.20
Purchase #3	$113.57	6.208%	$120.6204	$120.62	$120.60	$120.60
Purchase #4	$97.71	11.817%	$109.2564	$109.26	$109.25	$109.30
Purchase #5	$183.46	12.132%	$205.7174	$205.72	$205.70	$205.70
Purchase #6	$178.68	4.556%	$186.8207	$186.82	$186.80	$186.80
Purchase #7	$22.70	12.317%	$25.496	$25.50	$25.50	$25.50
7 purchase totals =	$870.14		$947.5732	$947.58	$947.50	$947.60