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	$39.84	4.737%	$41.7272	$41.73	$41.75	$41.70
Purchase #2	$79.38	4.542%	$82.9854	$82.99	$83.00	$83.00
Purchase #3	$132.65	5.711%	$140.2256	$140.23	$140.25	$140.20
Purchase #4	$41.85	11.251%	$46.5585	$46.56	$46.55	$46.60
Purchase #5	$107.72	13.699%	$122.4766	$122.48	$122.50	$122.50
Purchase #6	$107.91	3.279%	$111.4484	$111.45	$111.45	$111.40
Purchase #7	$112.37	4.216%	$117.1075	$117.11	$117.10	$117.10
7 purchase totals =	$621.72		$662.5292	$662.55	$662.60	$662.50