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	$244.84	10.235%	$269.8994	$269.90	$269.90	$269.90
Purchase #2	$127.64	7.859%	$137.6712	$137.67	$137.65	$137.70
Purchase #3	$106.67	6.806%	$113.93	$113.93	$113.95	$113.90
Purchase #4	$115.90	6.182%	$123.0649	$123.06	$123.05	$123.10
Purchase #5	$6.32	6.832%	$6.7518	$6.75	$6.75	$6.80
Purchase #6	$74.49	10.450%	$82.2742	$82.27	$82.25	$82.30
Purchase #7	$82.48	4.561%	$86.2419	$86.24	$86.25	$86.20
7 purchase totals =	$758.34		$819.8334	$819.82	$819.80	$819.90