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	$7.65	3.526%	$7.9197	$7.92	$7.90	$7.90
Purchase #2	$137.58	10.166%	$151.5664	$151.57	$151.55	$151.60
Purchase #3	$60.85	9.646%	$66.7196	$66.72	$66.70	$66.70
Purchase #4	$23.32	4.373%	$24.3398	$24.34	$24.35	$24.30
Purchase #5	$9.86	8.170%	$10.6656	$10.67	$10.65	$10.70
Purchase #6	$29.25	11.360%	$32.5728	$32.57	$32.55	$32.60
Purchase #7	$99.66	8.531%	$108.162	$108.16	$108.15	$108.20
7 purchase totals =	$368.17		$401.9459	$401.95	$401.85	$402.00