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	$78.97	13.422%	$89.5694	$89.57	$89.55	$89.60
Purchase #2	$216.48	6.220%	$229.9451	$229.95	$229.95	$229.90
Purchase #3	$199.42	4.661%	$208.715	$208.72	$208.70	$208.70
Purchase #4	$142.80	9.582%	$156.4831	$156.48	$156.50	$156.50
Purchase #5	$241.37	3.204%	$249.1035	$249.10	$249.10	$249.10
Purchase #6	$154.25	8.868%	$167.9289	$167.93	$167.95	$167.90
Purchase #7	$188.77	6.448%	$200.9419	$200.94	$200.95	$200.90
7 purchase totals =	$1,222.06		$1,302.6869	$1,302.69	$1,302.70	$1,302.60