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	$136.58	6.681%	$145.7049	$145.70	$145.70	$145.70
Purchase #2	$8.70	10.465%	$9.6105	$9.61	$9.60	$9.60
Purchase #3	$132.72	10.269%	$146.349	$146.35	$146.35	$146.30
Purchase #4	$87.40	13.691%	$99.3659	$99.37	$99.35	$99.40
Purchase #5	$49.75	10.378%	$54.9131	$54.91	$54.90	$54.90
Purchase #6	$48.72	13.725%	$55.4068	$55.41	$55.40	$55.40
Purchase #7	$37.63	10.197%	$41.4671	$41.47	$41.45	$41.50
7 purchase totals =	$501.50		$552.8173	$552.82	$552.75	$552.80