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	$42.30	13.480%	$48.002	$48.00	$48.00	$48.00
Purchase #2	$63.75	10.549%	$70.475	$70.48	$70.50	$70.50
Purchase #3	$103.51	6.103%	$109.8272	$109.83	$109.85	$109.80
Purchase #4	$99.62	9.406%	$108.9903	$108.99	$109.00	$109.00
Purchase #5	$48.55	12.731%	$54.7309	$54.73	$54.75	$54.70
Purchase #6	$243.32	5.148%	$255.8461	$255.85	$255.85	$255.80
Purchase #7	$79.66	8.360%	$86.3196	$86.32	$86.30	$86.30
7 purchase totals =	$680.71		$734.1911	$734.20	$734.25	$734.10