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	$172.55	3.309%	$178.2597	$178.26	$178.25	$178.30
Purchase #2	$57.27	8.803%	$62.3115	$62.31	$62.30	$62.30
Purchase #3	$54.27	3.303%	$56.0625	$56.06	$56.05	$56.10
Purchase #4	$98.26	10.763%	$108.8357	$108.84	$108.85	$108.80
Purchase #5	$108.73	7.542%	$116.9304	$116.93	$116.95	$116.90
Purchase #6	$61.78	9.717%	$67.7832	$67.78	$67.80	$67.80
Purchase #7	$62.78	7.176%	$67.2851	$67.29	$67.30	$67.30
7 purchase totals =	$615.64		$657.4681	$657.47	$657.50	$657.50