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	$132.27	9.172%	$144.4018	$144.40	$144.40	$144.40
Purchase #2	$228.73	11.243%	$254.4461	$254.45	$254.45	$254.40
Purchase #3	$83.65	3.417%	$86.5083	$86.51	$86.50	$86.50
Purchase #4	$86.98	6.142%	$92.3223	$92.32	$92.30	$92.30
Purchase #5	$168.62	11.528%	$188.0585	$188.06	$188.05	$188.10
Purchase #6	$68.89	5.821%	$72.9001	$72.90	$72.90	$72.90
Purchase #7	$46.90	13.514%	$53.2381	$53.24	$53.25	$53.20
7 purchase totals =	$816.04		$891.8752	$891.88	$891.85	$891.80