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	$10.78	11.610%	$12.0316	$12.03	$12.05	$12.00
Purchase #2	$151.96	4.540%	$158.859	$158.86	$158.85	$158.90
Purchase #3	$182.86	7.860%	$197.2328	$197.23	$197.25	$197.20
Purchase #4	$84.41	10.800%	$93.5263	$93.53	$93.55	$93.50
Purchase #5	$169.33	9.336%	$185.1386	$185.14	$185.15	$185.10
Purchase #6	$156.53	6.451%	$166.6278	$166.63	$166.65	$166.60
Purchase #7	$31.59	13.494%	$35.8528	$35.85	$35.85	$35.90
7 purchase totals =	$787.46		$849.2689	$849.27	$849.35	$849.20