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	$127.90	13.611%	$145.3085	$145.31	$145.30	$145.30
Purchase #2	$178.58	12.418%	$200.7561	$200.76	$200.75	$200.80
Purchase #3	$246.48	13.406%	$279.5231	$279.52	$279.50	$279.50
Purchase #4	$60.76	6.119%	$64.4779	$64.48	$64.50	$64.50
Purchase #5	$166.60	3.252%	$172.0178	$172.02	$172.00	$172.00
Purchase #6	$79.54	9.698%	$87.2538	$87.25	$87.25	$87.30
Purchase #7	$90.97	11.346%	$101.2915	$101.29	$101.30	$101.30
7 purchase totals =	$950.83		$1,050.6287	$1,050.63	$1,050.60	$1,050.70