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	$67.53	13.720%	$76.7951	$76.80	$76.80	$76.80
Purchase #2	$185.54	5.427%	$195.6093	$195.61	$195.60	$195.60
Purchase #3	$179.54	3.258%	$185.3894	$185.39	$185.40	$185.40
Purchase #4	$137.30	8.262%	$148.6437	$148.64	$148.65	$148.60
Purchase #5	$147.32	5.427%	$155.3151	$155.32	$155.30	$155.30
Purchase #6	$141.38	10.458%	$156.1655	$156.17	$156.15	$156.20
Purchase #7	$143.51	12.843%	$161.941	$161.94	$161.95	$161.90
7 purchase totals =	$1,002.12		$1,079.8591	$1,079.87	$1,079.85	$1,079.80