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	$87.87	11.856%	$98.2879	$98.29	$98.30	$98.30
Purchase #2	$109.41	3.117%	$112.8203	$112.82	$112.80	$112.80
Purchase #3	$180.75	4.442%	$188.7789	$188.78	$188.80	$188.80
Purchase #4	$200.62	9.636%	$219.9517	$219.95	$219.95	$220.00
Purchase #5	$112.91	13.501%	$128.154	$128.15	$128.15	$128.20
Purchase #6	$89.41	6.392%	$95.1251	$95.13	$95.15	$95.10
Purchase #7	$65.62	3.351%	$67.8189	$67.82	$67.80	$67.80
7 purchase totals =	$846.59		$910.9368	$910.94	$910.95	$911.00