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	$171.76	7.390%	$184.4531	$184.45	$184.45	$184.50
Purchase #2	$110.26	6.227%	$117.1259	$117.13	$117.15	$117.10
Purchase #3	$82.67	8.687%	$89.8515	$89.85	$89.85	$89.90
Purchase #4	$146.41	9.509%	$160.3321	$160.33	$160.35	$160.30
Purchase #5	$194.26	5.149%	$204.2624	$204.26	$204.25	$204.30
Purchase #6	$221.85	12.341%	$249.2285	$249.23	$249.25	$249.20
Purchase #7	$123.94	5.610%	$130.893	$130.89	$130.90	$130.90
7 purchase totals =	$1,051.15		$1,136.1465	$1,136.14	$1,136.20	$1,136.20