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	$75.54	3.733%	$78.3599	$78.36	$78.35	$78.40
Purchase #2	$41.38	5.398%	$43.6137	$43.61	$43.60	$43.60
Purchase #3	$81.51	4.181%	$84.9179	$84.92	$84.90	$84.90
Purchase #4	$80.77	6.150%	$85.7374	$85.74	$85.75	$85.70
Purchase #5	$59.71	6.670%	$63.6927	$63.69	$63.70	$63.70
Purchase #6	$147.92	7.588%	$159.1442	$159.14	$159.15	$159.10
Purchase #7	$52.72	5.394%	$55.5637	$55.56	$55.55	$55.60
7 purchase totals =	$539.55		$571.0295	$571.02	$571.00	$571.00