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	$169.27	6.643%	$180.5146	$180.51	$180.50	$180.50
Purchase #2	$32.83	9.702%	$36.0152	$36.02	$36.00	$36.00
Purchase #3	$34.96	6.695%	$37.3006	$37.30	$37.30	$37.30
Purchase #4	$57.59	12.137%	$64.5797	$64.58	$64.60	$64.60
Purchase #5	$127.94	6.678%	$136.4838	$136.48	$136.50	$136.50
Purchase #6	$196.54	12.528%	$221.1625	$221.16	$221.15	$221.20
Purchase #7	$204.52	8.852%	$222.6241	$222.62	$222.60	$222.60
7 purchase totals =	$823.65		$898.6805	$898.67	$898.65	$898.70