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	$11.93	3.868%	$12.3915	$12.39	$12.40	$12.40
Purchase #2	$209.26	4.739%	$219.1768	$219.18	$219.20	$219.20
Purchase #3	$109.43	6.394%	$116.427	$116.43	$116.45	$116.40
Purchase #4	$92.45	3.643%	$95.818	$95.82	$95.80	$95.80
Purchase #5	$78.55	9.315%	$85.8669	$85.87	$85.85	$85.90
Purchase #6	$179.60	7.265%	$192.6479	$192.65	$192.65	$192.60
Purchase #7	$110.37	7.653%	$118.8166	$118.82	$118.80	$118.80
7 purchase totals =	$791.59		$841.1447	$841.16	$841.15	$841.10