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	$142.39	12.733%	$160.5205	$160.52	$160.50	$160.50
Purchase #2	$155.61	5.625%	$164.3631	$164.36	$164.35	$164.40
Purchase #3	$23.38	3.723%	$24.2504	$24.25	$24.25	$24.30
Purchase #4	$131.51	7.483%	$141.3509	$141.35	$141.35	$141.40
Purchase #5	$76.39	9.202%	$83.4194	$83.42	$83.40	$83.40
Purchase #6	$161.87	4.258%	$168.7624	$168.76	$168.75	$168.80
Purchase #7	$75.65	10.327%	$83.4624	$83.46	$83.45	$83.50
7 purchase totals =	$766.80		$826.1291	$826.12	$826.05	$826.30