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	$36.98	11.852%	$41.3629	$41.36	$41.35	$41.40
Purchase #2	$88.32	12.102%	$99.0085	$99.01	$99.00	$99.00
Purchase #3	$78.51	13.784%	$89.3318	$89.33	$89.35	$89.30
Purchase #4	$146.74	13.415%	$166.4252	$166.43	$166.45	$166.40
Purchase #5	$127.94	6.141%	$135.7968	$135.80	$135.80	$135.80
Purchase #6	$222.98	11.597%	$248.839	$248.84	$248.85	$248.80
Purchase #7	$142.78	10.700%	$158.0575	$158.06	$158.05	$158.10
7 purchase totals =	$844.25		$938.8217	$938.83	$938.85	$938.80