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	$80.49	13.521%	$91.3731	$91.37	$91.35	$91.40
Purchase #2	$183.33	8.431%	$198.7866	$198.79	$198.80	$198.80
Purchase #3	$105.74	12.355%	$118.8042	$118.80	$118.80	$118.80
Purchase #4	$79.38	13.388%	$90.0074	$90.01	$90.00	$90.00
Purchase #5	$18.98	6.318%	$20.1792	$20.18	$20.20	$20.20
Purchase #6	$82.26	4.184%	$85.7018	$85.70	$85.70	$85.70
Purchase #7	$144.87	6.286%	$153.9765	$153.98	$154.00	$154.00
7 purchase totals =	$695.05		$758.8288	$758.83	$758.85	$758.90