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	$195.89	11.788%	$218.9815	$218.98	$219.00	$219.00
Purchase #2	$129.59	13.277%	$146.7957	$146.80	$146.80	$146.80
Purchase #3	$27.55	3.654%	$28.5567	$28.56	$28.55	$28.60
Purchase #4	$22.63	7.261%	$24.2732	$24.27	$24.25	$24.30
Purchase #5	$204.81	5.636%	$216.3531	$216.35	$216.35	$216.40
Purchase #6	$181.57	10.356%	$200.3734	$200.37	$200.35	$200.40
Purchase #7	$127.89	12.222%	$143.5207	$143.52	$143.50	$143.50
7 purchase totals =	$889.93		$978.8543	$978.85	$978.80	$979.00