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	$241.90	9.319%	$264.4427	$264.44	$264.45	$264.40
Purchase #2	$91.98	13.821%	$104.6926	$104.69	$104.70	$104.70
Purchase #3	$135.64	9.856%	$149.0087	$149.01	$149.00	$149.00
Purchase #4	$209.83	8.536%	$227.7411	$227.74	$227.75	$227.70
Purchase #5	$18.92	8.375%	$20.5046	$20.50	$20.50	$20.50
Purchase #6	$97.27	12.211%	$109.1476	$109.15	$109.15	$109.10
Purchase #7	$92.69	13.361%	$105.0743	$105.07	$105.05	$105.10
7 purchase totals =	$888.23		$980.6116	$980.60	$980.60	$980.50