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	$7.46	4.241%	$7.7764	$7.78	$7.80	$7.80
Purchase #2	$81.86	10.478%	$90.4373	$90.44	$90.45	$90.40
Purchase #3	$63.51	13.505%	$72.087	$72.09	$72.10	$72.10
Purchase #4	$57.93	12.390%	$65.1075	$65.11	$65.10	$65.10
Purchase #5	$82.25	8.811%	$89.497	$89.50	$89.50	$89.50
Purchase #6	$173.53	3.725%	$179.994	$179.99	$180.00	$180.00
Purchase #7	$170.56	11.840%	$190.7543	$190.75	$190.75	$190.80
7 purchase totals =	$637.10		$695.6535	$695.66	$695.70	$695.70