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	$57.49	4.170%	$59.8873	$59.89	$59.90	$59.90
Purchase #2	$52.50	4.214%	$54.7124	$54.71	$54.70	$54.70
Purchase #3	$39.88	13.214%	$45.1497	$45.15	$45.15	$45.10
Purchase #4	$70.39	6.279%	$74.8098	$74.81	$74.80	$74.80
Purchase #5	$139.33	6.798%	$148.8017	$148.80	$148.80	$148.80
Purchase #6	$244.69	4.304%	$255.2215	$255.22	$255.20	$255.20
Purchase #7	$109.83	8.113%	$118.7405	$118.74	$118.75	$118.70
7 purchase totals =	$714.11		$757.3229	$757.32	$757.30	$757.20