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	$128.51	11.108%	$142.7849	$142.78	$142.80	$142.80
Purchase #2	$231.37	10.249%	$255.0831	$255.08	$255.10	$255.10
Purchase #3	$93.90	5.416%	$98.9856	$98.99	$99.00	$99.00
Purchase #4	$46.83	7.453%	$50.3202	$50.32	$50.30	$50.30
Purchase #5	$134.53	6.642%	$143.4655	$143.47	$143.45	$143.50
Purchase #6	$105.27	9.318%	$115.0791	$115.08	$115.10	$115.10
Purchase #7	$85.28	10.306%	$94.069	$94.07	$94.05	$94.10
7 purchase totals =	$825.69		$899.7874	$899.79	$899.80	$899.90