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	$51.61	4.430%	$53.8963	$53.90	$53.90	$53.90
Purchase #2	$82.99	9.495%	$90.8699	$90.87	$90.85	$90.90
Purchase #3	$116.87	9.438%	$127.9002	$127.90	$127.90	$127.90
Purchase #4	$11.73	12.303%	$13.1731	$13.17	$13.15	$13.20
Purchase #5	$96.28	4.693%	$100.7984	$100.80	$100.80	$100.80
Purchase #6	$41.50	12.679%	$46.7618	$46.76	$46.75	$46.80
Purchase #7	$97.97	11.517%	$109.2532	$109.25	$109.25	$109.30
7 purchase totals =	$498.95		$542.6529	$542.65	$542.60	$542.80