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	$128.53	8.545%	$139.5129	$139.51	$139.50	$139.50
Purchase #2	$220.62	3.742%	$228.8756	$228.88	$228.90	$228.90
Purchase #3	$17.51	5.840%	$18.5326	$18.53	$18.55	$18.50
Purchase #4	$38.33	6.563%	$40.8456	$40.85	$40.85	$40.80
Purchase #5	$65.62	6.182%	$69.6766	$69.68	$69.70	$69.70
Purchase #6	$158.72	5.528%	$167.494	$167.49	$167.50	$167.50
Purchase #7	$248.59	8.196%	$268.9644	$268.96	$268.95	$269.00
7 purchase totals =	$877.92		$933.9017	$933.90	$933.95	$933.90