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	$146.40	6.159%	$155.4168	$155.42	$155.40	$155.40
Purchase #2	$195.72	5.298%	$206.0892	$206.09	$206.10	$206.10
Purchase #3	$210.45	6.178%	$223.4516	$223.45	$223.45	$223.50
Purchase #4	$120.43	8.719%	$130.9303	$130.93	$130.95	$130.90
Purchase #5	$185.53	8.228%	$200.7954	$200.80	$200.80	$200.80
Purchase #6	$130.94	6.702%	$139.7156	$139.72	$139.70	$139.70
Purchase #7	$158.63	6.610%	$169.1154	$169.12	$169.10	$169.10
7 purchase totals =	$1,148.10		$1,225.5143	$1,225.53	$1,225.50	$1,225.50