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	$102.39	9.631%	$112.2512	$112.25	$112.25	$112.30
Purchase #2	$243.77	3.839%	$253.1283	$253.13	$253.15	$253.10
Purchase #3	$198.29	12.303%	$222.6856	$222.69	$222.70	$222.70
Purchase #4	$229.90	8.509%	$249.4622	$249.46	$249.45	$249.50
Purchase #5	$133.47	9.592%	$146.2724	$146.27	$146.25	$146.30
Purchase #6	$41.89	8.752%	$45.5562	$45.56	$45.55	$45.60
Purchase #7	$200.26	6.623%	$213.5232	$213.52	$213.50	$213.50
7 purchase totals =	$1,149.97		$1,242.8791	$1,242.88	$1,242.85	$1,243.00