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	$46.70	10.264%	$51.4933	$51.49	$51.50	$51.50
Purchase #2	$11.56	6.288%	$12.2869	$12.29	$12.30	$12.30
Purchase #3	$139.63	13.491%	$158.4675	$158.47	$158.45	$158.50
Purchase #4	$181.89	3.586%	$188.4126	$188.41	$188.40	$188.40
Purchase #5	$172.44	5.588%	$182.0759	$182.08	$182.10	$182.10
Purchase #6	$126.55	11.304%	$140.8552	$140.86	$140.85	$140.90
Purchase #7	$181.27	8.303%	$196.3208	$196.32	$196.30	$196.30
7 purchase totals =	$860.04		$929.9122	$929.92	$929.90	$930.00