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	$164.60	8.319%	$178.2931	$178.29	$178.30	$178.30
Purchase #2	$180.43	4.714%	$188.9355	$188.94	$188.95	$188.90
Purchase #3	$85.51	10.206%	$94.2372	$94.24	$94.25	$94.20
Purchase #4	$181.88	10.252%	$200.5263	$200.53	$200.55	$200.50
Purchase #5	$82.73	6.813%	$88.3664	$88.37	$88.35	$88.40
Purchase #6	$238.96	11.762%	$267.0665	$267.07	$267.05	$267.10
Purchase #7	$45.92	5.233%	$48.323	$48.32	$48.30	$48.30
7 purchase totals =	$980.03		$1,065.7480	$1,065.76	$1,065.75	$1,065.70