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	$230.76	10.684%	$255.4144	$255.41	$255.40	$255.40
Purchase #2	$226.83	12.766%	$255.7871	$255.79	$255.80	$255.80
Purchase #3	$164.98	9.828%	$181.1942	$181.19	$181.20	$181.20
Purchase #4	$250.45	13.503%	$284.2683	$284.27	$284.25	$284.30
Purchase #5	$40.34	9.563%	$44.1977	$44.20	$44.20	$44.20
Purchase #6	$152.96	9.478%	$167.4575	$167.46	$167.45	$167.50
Purchase #7	$79.66	9.280%	$87.0524	$87.05	$87.05	$87.10
7 purchase totals =	$1,145.98		$1,275.3716	$1,275.37	$1,275.35	$1,275.50