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	$120.61	7.466%	$129.6147	$129.61	$129.60	$129.60
Purchase #2	$102.43	6.277%	$108.8595	$108.86	$108.85	$108.90
Purchase #3	$68.33	3.313%	$70.5938	$70.59	$70.60	$70.60
Purchase #4	$119.56	4.138%	$124.5074	$124.51	$124.50	$124.50
Purchase #5	$226.31	12.826%	$255.3365	$255.34	$255.35	$255.30
Purchase #6	$234.63	5.840%	$248.3324	$248.33	$248.35	$248.30
Purchase #7	$119.59	6.348%	$127.1816	$127.18	$127.20	$127.20
7 purchase totals =	$991.46		$1,064.4259	$1,064.42	$1,064.45	$1,064.40