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	$91.56	7.283%	$98.2283	$98.23	$98.25	$98.20
Purchase #2	$142.33	9.208%	$155.4357	$155.44	$155.45	$155.40
Purchase #3	$86.72	13.612%	$98.5243	$98.52	$98.50	$98.50
Purchase #4	$132.64	5.285%	$139.65	$139.65	$139.65	$139.70
Purchase #5	$32.90	5.541%	$34.723	$34.72	$34.70	$34.70
Purchase #6	$56.63	5.425%	$59.7022	$59.70	$59.70	$59.70
Purchase #7	$74.58	9.275%	$81.4973	$81.50	$81.50	$81.50
7 purchase totals =	$617.36		$667.7608	$667.76	$667.75	$667.70