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	$87.81	3.491%	$90.8754	$90.88	$90.90	$90.90
Purchase #2	$172.90	4.826%	$181.2442	$181.24	$181.25	$181.20
Purchase #3	$186.76	13.330%	$211.6551	$211.66	$211.65	$211.70
Purchase #4	$21.72	3.718%	$22.5275	$22.53	$22.55	$22.50
Purchase #5	$99.28	8.672%	$107.8896	$107.89	$107.90	$107.90
Purchase #6	$57.76	12.138%	$64.7709	$64.77	$64.75	$64.80
Purchase #7	$128.37	6.264%	$136.4111	$136.41	$136.40	$136.40
7 purchase totals =	$754.60		$815.3738	$815.38	$815.40	$815.40