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	$39.47	7.524%	$42.4397	$42.44	$42.45	$42.40
Purchase #2	$19.55	9.539%	$21.4149	$21.41	$21.40	$21.40
Purchase #3	$111.92	13.516%	$127.0471	$127.05	$127.05	$127.00
Purchase #4	$155.33	7.562%	$167.0761	$167.08	$167.10	$167.10
Purchase #5	$233.67	5.537%	$246.6083	$246.61	$246.60	$246.60
Purchase #6	$208.44	10.225%	$229.753	$229.75	$229.75	$229.80
Purchase #7	$29.71	5.707%	$31.4055	$31.41	$31.40	$31.40
7 purchase totals =	$798.09		$865.7446	$865.75	$865.75	$865.70