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	$86.47	7.427%	$92.8921	$92.89	$92.90	$92.90
Purchase #2	$153.34	8.324%	$166.104	$166.10	$166.10	$166.10
Purchase #3	$165.30	13.599%	$187.7791	$187.78	$187.80	$187.80
Purchase #4	$79.65	12.695%	$89.7616	$89.76	$89.75	$89.80
Purchase #5	$168.38	5.737%	$178.04	$178.04	$178.05	$178.00
Purchase #6	$54.85	3.730%	$56.8959	$56.90	$56.90	$56.90
Purchase #7	$188.88	12.563%	$212.609	$212.61	$212.60	$212.60
7 purchase totals =	$896.87		$984.0817	$984.08	$984.10	$984.10