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	$110.95	5.353%	$116.8892	$116.89	$116.90	$116.90
Purchase #2	$211.98	10.782%	$234.8357	$234.84	$234.85	$234.80
Purchase #3	$29.83	12.493%	$33.5567	$33.56	$33.55	$33.60
Purchase #4	$129.72	7.694%	$139.7007	$139.70	$139.70	$139.70
Purchase #5	$63.96	4.669%	$66.9463	$66.95	$66.95	$66.90
Purchase #6	$125.88	10.662%	$139.3013	$139.30	$139.30	$139.30
Purchase #7	$96.83	5.602%	$102.2544	$102.25	$102.25	$102.30
7 purchase totals =	$769.15		$833.4843	$833.49	$833.50	$833.50