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	$35.50	8.829%	$38.6343	$38.63	$38.65	$38.60
Purchase #2	$148.51	9.701%	$162.917	$162.92	$162.90	$162.90
Purchase #3	$144.48	5.170%	$151.9496	$151.95	$151.95	$151.90
Purchase #4	$70.49	5.853%	$74.6158	$74.62	$74.60	$74.60
Purchase #5	$9.90	9.118%	$10.8027	$10.80	$10.80	$10.80
Purchase #6	$33.67	11.416%	$37.5138	$37.51	$37.50	$37.50
Purchase #7	$168.60	10.591%	$186.4564	$186.46	$186.45	$186.50
7 purchase totals =	$611.15		$662.8896	$662.89	$662.85	$662.80