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	$145.84	13.453%	$165.4599	$165.46	$165.45	$165.50
Purchase #2	$45.36	6.150%	$48.1496	$48.15	$48.15	$48.10
Purchase #3	$39.56	12.136%	$44.361	$44.36	$44.35	$44.40
Purchase #4	$220.53	7.828%	$237.7931	$237.79	$237.80	$237.80
Purchase #5	$52.72	13.172%	$59.6643	$59.66	$59.65	$59.70
Purchase #6	$67.99	5.310%	$71.6003	$71.60	$71.60	$71.60
Purchase #7	$153.87	10.212%	$169.5832	$169.58	$169.60	$169.60
7 purchase totals =	$725.87		$796.6114	$796.60	$796.60	$796.70