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	$144.95	6.753%	$154.7385	$154.74	$154.75	$154.70
Purchase #2	$112.86	4.820%	$118.2999	$118.30	$118.30	$118.30
Purchase #3	$160.48	8.739%	$174.5043	$174.50	$174.50	$174.50
Purchase #4	$25.66	8.589%	$27.8639	$27.86	$27.85	$27.90
Purchase #5	$127.59	9.503%	$139.7149	$139.71	$139.70	$139.70
Purchase #6	$11.66	9.646%	$12.7847	$12.78	$12.80	$12.80
Purchase #7	$240.28	6.229%	$255.247	$255.25	$255.25	$255.20
7 purchase totals =	$823.48		$883.1532	$883.14	$883.15	$883.10