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	$95.34	4.616%	$99.7409	$99.74	$99.75	$99.70
Purchase #2	$29.50	9.547%	$32.3164	$32.32	$32.30	$32.30
Purchase #3	$79.27	4.131%	$82.5446	$82.54	$82.55	$82.50
Purchase #4	$100.28	3.704%	$103.9944	$103.99	$104.00	$104.00
Purchase #5	$30.42	10.369%	$33.5742	$33.57	$33.55	$33.60
Purchase #6	$158.42	8.596%	$172.0378	$172.04	$172.05	$172.00
Purchase #7	$164.62	9.519%	$180.2902	$180.29	$180.30	$180.30
7 purchase totals =	$657.85		$704.4985	$704.49	$704.50	$704.40