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	$150.49	3.223%	$155.3403	$155.34	$155.35	$155.30
Purchase #2	$246.89	12.655%	$278.1339	$278.13	$278.15	$278.10
Purchase #3	$187.67	13.136%	$212.3223	$212.32	$212.30	$212.30
Purchase #4	$146.35	3.535%	$151.5235	$151.52	$151.50	$151.50
Purchase #5	$94.77	3.277%	$97.8756	$97.88	$97.90	$97.90
Purchase #6	$149.89	4.412%	$156.5031	$156.50	$156.50	$156.50
Purchase #7	$151.78	4.823%	$159.1003	$159.10	$159.10	$159.10
7 purchase totals =	$1,127.84		$1,210.7990	$1,210.79	$1,210.80	$1,210.70