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	$19.67	7.647%	$21.1742	$21.17	$21.15	$21.20
Purchase #2	$96.41	4.467%	$100.7166	$100.72	$100.70	$100.70
Purchase #3	$23.67	3.699%	$24.5456	$24.55	$24.55	$24.50
Purchase #4	$209.65	3.665%	$217.3337	$217.33	$217.35	$217.30
Purchase #5	$141.39	3.577%	$146.4475	$146.45	$146.45	$146.40
Purchase #6	$240.30	11.111%	$266.9997	$267.00	$267.00	$267.00
Purchase #7	$83.25	8.237%	$90.1073	$90.11	$90.10	$90.10
7 purchase totals =	$814.34		$867.3246	$867.33	$867.30	$867.20