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	$57.93	6.792%	$61.8646	$61.86	$61.85	$61.90
Purchase #2	$25.49	12.436%	$28.6599	$28.66	$28.65	$28.70
Purchase #3	$205.79	10.870%	$228.1594	$228.16	$228.15	$228.20
Purchase #4	$220.69	3.784%	$229.0409	$229.04	$229.05	$229.00
Purchase #5	$81.88	8.840%	$89.1182	$89.12	$89.10	$89.10
Purchase #6	$225.35	11.381%	$250.9971	$251.00	$251.00	$251.00
Purchase #7	$56.63	5.139%	$59.5402	$59.54	$59.55	$59.50
7 purchase totals =	$873.76		$947.3803	$947.38	$947.35	$947.40