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	$133.59	4.341%	$139.3891	$139.39	$139.40	$139.40
Purchase #2	$250.38	11.396%	$278.9133	$278.91	$278.90	$278.90
Purchase #3	$57.49	13.780%	$65.4121	$65.41	$65.40	$65.40
Purchase #4	$43.61	10.681%	$48.268	$48.27	$48.25	$48.30
Purchase #5	$80.80	12.417%	$90.8329	$90.83	$90.85	$90.80
Purchase #6	$92.70	5.234%	$97.5519	$97.55	$97.55	$97.60
Purchase #7	$7.96	10.115%	$8.7652	$8.77	$8.75	$8.80
7 purchase totals =	$666.53		$729.1325	$729.13	$729.10	$729.20