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	$16.71	10.262%	$18.4248	$18.42	$18.40	$18.40
Purchase #2	$37.86	6.693%	$40.394	$40.39	$40.40	$40.40
Purchase #3	$154.33	12.810%	$174.0997	$174.10	$174.10	$174.10
Purchase #4	$161.96	10.445%	$178.8767	$178.88	$178.90	$178.90
Purchase #5	$80.71	12.566%	$90.852	$90.85	$90.85	$90.90
Purchase #6	$70.48	9.149%	$76.9282	$76.93	$76.95	$76.90
Purchase #7	$94.92	4.257%	$98.9607	$98.96	$98.95	$99.00
7 purchase totals =	$616.97		$678.5361	$678.53	$678.55	$678.60