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	$122.85	4.864%	$128.8254	$128.83	$128.85	$128.80
Purchase #2	$139.43	5.562%	$147.1851	$147.19	$147.20	$147.20
Purchase #3	$116.56	9.627%	$127.7812	$127.78	$127.80	$127.80
Purchase #4	$133.78	10.658%	$148.0383	$148.04	$148.05	$148.00
Purchase #5	$84.98	5.799%	$89.908	$89.91	$89.90	$89.90
Purchase #6	$105.45	10.217%	$116.2238	$116.22	$116.20	$116.20
Purchase #7	$141.75	6.555%	$151.0417	$151.04	$151.05	$151.00
7 purchase totals =	$844.80		$909.0035	$909.01	$909.05	$908.90