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	$123.72	11.680%	$138.1705	$138.17	$138.15	$138.20
Purchase #2	$242.83	4.693%	$254.226	$254.23	$254.25	$254.20
Purchase #3	$232.53	4.320%	$242.5753	$242.58	$242.60	$242.60
Purchase #4	$117.40	6.742%	$125.3151	$125.32	$125.30	$125.30
Purchase #5	$88.28	13.145%	$99.8844	$99.88	$99.90	$99.90
Purchase #6	$185.39	13.382%	$210.1989	$210.20	$210.20	$210.20
Purchase #7	$155.78	4.519%	$162.8197	$162.82	$162.80	$162.80
7 purchase totals =	$1,145.93		$1,233.1899	$1,233.20	$1,233.20	$1,233.20