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	$80.56	9.865%	$88.5072	$88.51	$88.50	$88.50
Purchase #2	$84.68	9.463%	$92.6933	$92.69	$92.70	$92.70
Purchase #3	$127.60	4.786%	$133.7069	$133.71	$133.70	$133.70
Purchase #4	$95.97	13.621%	$109.0421	$109.04	$109.05	$109.00
Purchase #5	$33.35	13.662%	$37.9063	$37.91	$37.90	$37.90
Purchase #6	$167.41	5.332%	$176.3363	$176.34	$176.35	$176.30
Purchase #7	$38.35	10.659%	$42.4377	$42.44	$42.45	$42.40
7 purchase totals =	$627.92		$680.6298	$680.64	$680.65	$680.50