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	$236.93	5.202%	$249.2551	$249.26	$249.25	$249.30
Purchase #2	$123.85	6.515%	$131.9188	$131.92	$131.90	$131.90
Purchase #3	$21.57	7.873%	$23.2682	$23.27	$23.25	$23.30
Purchase #4	$74.70	8.472%	$81.0286	$81.03	$81.05	$81.00
Purchase #5	$129.52	12.118%	$145.2152	$145.22	$145.20	$145.20
Purchase #6	$101.50	11.616%	$113.2902	$113.29	$113.30	$113.30
Purchase #7	$89.25	12.371%	$100.2911	$100.29	$100.30	$100.30
7 purchase totals =	$777.32		$844.2672	$844.28	$844.25	$844.30