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	$128.92	5.161%	$135.5736	$135.57	$135.55	$135.60
Purchase #2	$222.96	8.357%	$241.5928	$241.59	$241.60	$241.60
Purchase #3	$20.72	6.694%	$22.107	$22.11	$22.10	$22.10
Purchase #4	$177.59	7.169%	$190.3214	$190.32	$190.30	$190.30
Purchase #5	$50.91	4.756%	$53.3313	$53.33	$53.35	$53.30
Purchase #6	$117.56	8.465%	$127.5115	$127.51	$127.50	$127.50
Purchase #7	$224.32	10.661%	$248.2348	$248.23	$248.25	$248.20
7 purchase totals =	$942.98		$1,018.6724	$1,018.66	$1,018.65	$1,018.60