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	$39.86	3.310%	$41.1794	$41.18	$41.20	$41.20
Purchase #2	$53.34	8.575%	$57.9139	$57.91	$57.90	$57.90
Purchase #3	$135.36	7.566%	$145.6013	$145.60	$145.60	$145.60
Purchase #4	$58.58	13.222%	$66.3254	$66.33	$66.35	$66.30
Purchase #5	$107.69	6.222%	$114.3905	$114.39	$114.40	$114.40
Purchase #6	$144.25	13.375%	$163.5434	$163.54	$163.55	$163.50
Purchase #7	$69.48	13.274%	$78.7028	$78.70	$78.70	$78.70
7 purchase totals =	$608.56		$667.6567	$667.65	$667.70	$667.60