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	$71.65	13.225%	$81.1257	$81.13	$81.15	$81.10
Purchase #2	$61.75	7.184%	$66.1861	$66.19	$66.20	$66.20
Purchase #3	$166.48	12.742%	$187.6929	$187.69	$187.70	$187.70
Purchase #4	$130.31	10.841%	$144.4369	$144.44	$144.45	$144.40
Purchase #5	$39.32	5.159%	$41.3485	$41.35	$41.35	$41.30
Purchase #6	$32.32	11.846%	$36.1486	$36.15	$36.15	$36.10
Purchase #7	$63.35	11.457%	$70.608	$70.61	$70.60	$70.60
7 purchase totals =	$565.18		$627.5467	$627.56	$627.60	$627.40