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	$46.82	5.844%	$49.5562	$49.56	$49.55	$49.60
Purchase #2	$44.86	11.791%	$50.1494	$50.15	$50.15	$50.10
Purchase #3	$34.56	12.281%	$38.8043	$38.80	$38.80	$38.80
Purchase #4	$38.33	12.130%	$42.9794	$42.98	$43.00	$43.00
Purchase #5	$128.56	8.187%	$139.0852	$139.09	$139.10	$139.10
Purchase #6	$159.74	8.514%	$173.3403	$173.34	$173.35	$173.30
Purchase #7	$182.95	7.220%	$196.159	$196.16	$196.15	$196.20
7 purchase totals =	$635.82		$690.0738	$690.08	$690.10	$690.10