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	$250.25	12.622%	$281.8366	$281.84	$281.85	$281.80
Purchase #2	$165.86	13.526%	$188.2942	$188.29	$188.30	$188.30
Purchase #3	$18.76	6.806%	$20.0368	$20.04	$20.05	$20.00
Purchase #4	$18.30	12.722%	$20.6281	$20.63	$20.65	$20.60
Purchase #5	$30.34	9.469%	$33.2129	$33.21	$33.20	$33.20
Purchase #6	$18.67	11.556%	$20.8275	$20.83	$20.85	$20.80
Purchase #7	$239.93	4.607%	$250.9836	$250.98	$251.00	$251.00
7 purchase totals =	$742.11		$815.8197	$815.82	$815.90	$815.70