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	$182.59	3.501%	$188.9825	$188.98	$189.00	$189.00
Purchase #2	$47.77	13.602%	$54.2677	$54.27	$54.25	$54.30
Purchase #3	$37.97	8.168%	$41.0714	$41.07	$41.05	$41.10
Purchase #4	$134.30	8.813%	$146.1359	$146.14	$146.15	$146.10
Purchase #5	$146.38	9.210%	$159.8616	$159.86	$159.85	$159.90
Purchase #6	$141.31	11.430%	$157.4617	$157.46	$157.45	$157.50
Purchase #7	$80.39	6.417%	$85.5486	$85.55	$85.55	$85.50
7 purchase totals =	$770.71		$833.3294	$833.33	$833.30	$833.40