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	$81.57	11.748%	$91.1528	$91.15	$91.15	$91.20
Purchase #2	$35.74	8.139%	$38.6489	$38.65	$38.65	$38.60
Purchase #3	$68.46	6.749%	$73.0804	$73.08	$73.10	$73.10
Purchase #4	$138.69	9.802%	$152.2844	$152.28	$152.30	$152.30
Purchase #5	$167.38	11.707%	$186.9752	$186.98	$187.00	$187.00
Purchase #6	$85.86	4.572%	$89.7855	$89.79	$89.80	$89.80
Purchase #7	$236.37	12.755%	$266.519	$266.52	$266.50	$266.50
7 purchase totals =	$814.07		$898.4462	$898.45	$898.50	$898.50