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	$65.45	8.521%	$71.027	$71.03	$71.05	$71.00
Purchase #2	$130.39	10.122%	$143.5881	$143.59	$143.60	$143.60
Purchase #3	$152.90	12.613%	$172.1853	$172.19	$172.20	$172.20
Purchase #4	$148.86	13.778%	$169.3699	$169.37	$169.35	$169.40
Purchase #5	$49.56	8.738%	$53.8906	$53.89	$53.90	$53.90
Purchase #6	$176.69	7.727%	$190.3428	$190.34	$190.35	$190.30
Purchase #7	$44.48	10.445%	$49.1259	$49.13	$49.15	$49.10
7 purchase totals =	$768.33		$849.5296	$849.54	$849.60	$849.50