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	$26.51	3.196%	$27.3573	$27.36	$27.35	$27.40
Purchase #2	$249.41	6.212%	$264.9033	$264.90	$264.90	$264.90
Purchase #3	$138.70	5.120%	$145.8014	$145.80	$145.80	$145.80
Purchase #4	$133.72	8.304%	$144.8241	$144.82	$144.80	$144.80
Purchase #5	$85.27	6.418%	$90.7426	$90.74	$90.75	$90.70
Purchase #6	$173.58	5.487%	$183.1043	$183.10	$183.10	$183.10
Purchase #7	$164.66	4.314%	$171.7634	$171.76	$171.75	$171.80
7 purchase totals =	$971.85		$1,028.4964	$1,028.48	$1,028.45	$1,028.50