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	$227.86	11.834%	$254.825	$254.83	$254.85	$254.80
Purchase #2	$60.52	6.752%	$64.6063	$64.61	$64.60	$64.60
Purchase #3	$66.29	7.510%	$71.2684	$71.27	$71.25	$71.30
Purchase #4	$101.46	13.354%	$115.009	$115.01	$115.00	$115.00
Purchase #5	$118.87	9.415%	$130.0616	$130.06	$130.05	$130.10
Purchase #6	$41.32	11.169%	$45.935	$45.94	$45.95	$45.90
Purchase #7	$236.98	8.804%	$257.8437	$257.84	$257.85	$257.80
7 purchase totals =	$853.30		$939.5490	$939.56	$939.55	$939.50