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	$155.77	12.605%	$175.4048	$175.40	$175.40	$175.40
Purchase #2	$140.27	4.613%	$146.7407	$146.74	$146.75	$146.70
Purchase #3	$78.37	9.349%	$85.6968	$85.70	$85.70	$85.70
Purchase #4	$196.45	11.699%	$219.4327	$219.43	$219.45	$219.40
Purchase #5	$128.44	13.557%	$145.8526	$145.85	$145.85	$145.90
Purchase #6	$72.48	10.107%	$79.8056	$79.81	$79.80	$79.80
Purchase #7	$38.37	5.523%	$40.4892	$40.49	$40.50	$40.50
7 purchase totals =	$810.15		$893.4224	$893.42	$893.45	$893.40