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	$20.94	3.660%	$21.7064	$21.71	$21.70	$21.70
Purchase #2	$39.65	6.291%	$42.1444	$42.14	$42.15	$42.10
Purchase #3	$68.87	4.753%	$72.1434	$72.14	$72.15	$72.10
Purchase #4	$92.42	6.747%	$98.6556	$98.66	$98.65	$98.70
Purchase #5	$40.91	11.805%	$45.7394	$45.74	$45.75	$45.70
Purchase #6	$50.55	11.170%	$56.1964	$56.20	$56.20	$56.20
Purchase #7	$156.31	10.253%	$172.3365	$172.34	$172.35	$172.30
7 purchase totals =	$469.65		$508.9221	$508.93	$508.95	$508.80