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	$205.83	8.302%	$222.918	$222.92	$222.90	$222.90
Purchase #2	$231.96	13.189%	$262.5532	$262.55	$262.55	$262.60
Purchase #3	$20.43	4.559%	$21.3614	$21.36	$21.35	$21.40
Purchase #4	$214.56	6.315%	$228.1095	$228.11	$228.10	$228.10
Purchase #5	$68.69	13.610%	$78.0387	$78.04	$78.05	$78.00
Purchase #6	$184.78	12.255%	$207.4248	$207.42	$207.40	$207.40
Purchase #7	$79.52	3.700%	$82.4622	$82.46	$82.45	$82.50
7 purchase totals =	$1,005.77		$1,102.8678	$1,102.86	$1,102.80	$1,102.90