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	$9.55	13.338%	$10.8238	$10.82	$10.80	$10.80
Purchase #2	$61.69	4.426%	$64.4204	$64.42	$64.40	$64.40
Purchase #3	$142.45	6.157%	$151.2206	$151.22	$151.20	$151.20
Purchase #4	$184.66	5.355%	$194.5485	$194.55	$194.55	$194.50
Purchase #5	$130.90	7.597%	$140.8445	$140.84	$140.85	$140.80
Purchase #6	$219.50	12.262%	$246.4151	$246.42	$246.40	$246.40
Purchase #7	$196.41	13.218%	$222.3715	$222.37	$222.35	$222.40
7 purchase totals =	$945.16		$1,030.6444	$1,030.64	$1,030.55	$1,030.50