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	$242.53	4.654%	$253.8173	$253.82	$253.80	$253.80
Purchase #2	$182.66	9.802%	$200.5643	$200.56	$200.55	$200.60
Purchase #3	$62.87	5.820%	$66.529	$66.53	$66.55	$66.50
Purchase #4	$140.92	12.870%	$159.0564	$159.06	$159.05	$159.10
Purchase #5	$24.94	10.675%	$27.6023	$27.60	$27.60	$27.60
Purchase #6	$27.42	4.479%	$28.6481	$28.65	$28.65	$28.60
Purchase #7	$137.87	12.613%	$155.2595	$155.26	$155.25	$155.30
7 purchase totals =	$819.21		$891.4769	$891.48	$891.45	$891.50