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	$242.85	11.585%	$270.9842	$270.98	$271.00	$271.00
Purchase #2	$95.31	4.336%	$99.4426	$99.44	$99.45	$99.40
Purchase #3	$67.49	4.213%	$70.3334	$70.33	$70.35	$70.30
Purchase #4	$167.82	4.523%	$175.4105	$175.41	$175.40	$175.40
Purchase #5	$12.88	12.766%	$14.5243	$14.52	$14.50	$14.50
Purchase #6	$249.97	5.509%	$263.7408	$263.74	$263.75	$263.70
Purchase #7	$196.69	12.710%	$221.6893	$221.69	$221.70	$221.70
7 purchase totals =	$1,033.01		$1,116.1251	$1,116.11	$1,116.15	$1,116.00