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	$123.30	5.858%	$130.5229	$130.52	$130.50	$130.50
Purchase #2	$177.52	6.822%	$189.6304	$189.63	$189.65	$189.60
Purchase #3	$230.61	3.598%	$238.9073	$238.91	$238.90	$238.90
Purchase #4	$113.56	11.199%	$126.2776	$126.28	$126.30	$126.30
Purchase #5	$200.57	9.451%	$219.5259	$219.53	$219.55	$219.50
Purchase #6	$78.83	4.593%	$82.4507	$82.45	$82.45	$82.50
Purchase #7	$66.93	11.643%	$74.7227	$74.72	$74.70	$74.70
7 purchase totals =	$991.32		$1,062.0375	$1,062.04	$1,062.05	$1,062.00