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	$85.60	7.796%	$92.2734	$92.27	$92.25	$92.30
Purchase #2	$91.55	5.630%	$96.7043	$96.70	$96.70	$96.70
Purchase #3	$238.73	4.329%	$249.0646	$249.06	$249.05	$249.10
Purchase #4	$141.49	6.840%	$151.1679	$151.17	$151.15	$151.20
Purchase #5	$56.66	9.208%	$61.8773	$61.88	$61.90	$61.90
Purchase #6	$167.78	7.188%	$179.84	$179.84	$179.85	$179.80
Purchase #7	$152.95	7.812%	$164.8985	$164.90	$164.90	$164.90
7 purchase totals =	$934.76		$995.8260	$995.82	$995.80	$995.90