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	$87.64	13.176%	$99.1874	$99.19	$99.20	$99.20
Purchase #2	$51.77	10.710%	$57.3146	$57.31	$57.30	$57.30
Purchase #3	$53.98	13.782%	$61.4195	$61.42	$61.40	$61.40
Purchase #4	$146.74	10.738%	$162.4969	$162.50	$162.50	$162.50
Purchase #5	$64.38	13.136%	$72.837	$72.84	$72.85	$72.80
Purchase #6	$202.58	10.260%	$223.3647	$223.36	$223.35	$223.40
Purchase #7	$128.82	7.192%	$138.0847	$138.08	$138.10	$138.10
7 purchase totals =	$735.91		$814.7048	$814.70	$814.70	$814.70