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	$227.64	5.410%	$239.9553	$239.96	$239.95	$240.00
Purchase #2	$163.92	12.537%	$184.4707	$184.47	$184.45	$184.50
Purchase #3	$81.56	11.369%	$90.8326	$90.83	$90.85	$90.80
Purchase #4	$172.65	7.544%	$185.6747	$185.67	$185.65	$185.70
Purchase #5	$28.40	11.359%	$31.626	$31.63	$31.65	$31.60
Purchase #6	$156.36	6.128%	$165.9417	$165.94	$165.95	$165.90
Purchase #7	$45.50	6.251%	$48.3442	$48.34	$48.35	$48.30
7 purchase totals =	$876.03		$946.8452	$946.84	$946.85	$946.80