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	$46.90	7.432%	$50.3856	$50.39	$50.40	$50.40
Purchase #2	$93.34	8.809%	$101.5623	$101.56	$101.55	$101.60
Purchase #3	$93.46	7.197%	$100.1863	$100.19	$100.20	$100.20
Purchase #4	$89.78	13.357%	$101.7719	$101.77	$101.75	$101.80
Purchase #5	$84.90	6.218%	$90.1791	$90.18	$90.20	$90.20
Purchase #6	$119.95	6.264%	$127.4637	$127.46	$127.45	$127.50
Purchase #7	$122.40	12.421%	$137.6033	$137.60	$137.60	$137.60
7 purchase totals =	$650.73		$709.1522	$709.15	$709.15	$709.30