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	$79.61	11.624%	$88.8639	$88.86	$88.85	$88.90
Purchase #2	$112.30	11.194%	$124.8709	$124.87	$124.85	$124.90
Purchase #3	$87.76	8.832%	$95.511	$95.51	$95.50	$95.50
Purchase #4	$145.33	11.632%	$162.2348	$162.23	$162.25	$162.20
Purchase #5	$74.92	5.195%	$78.8121	$78.81	$78.80	$78.80
Purchase #6	$92.58	13.777%	$105.3347	$105.33	$105.35	$105.30
Purchase #7	$217.94	5.207%	$229.2881	$229.29	$229.30	$229.30
7 purchase totals =	$810.44		$884.9155	$884.90	$884.90	$884.90