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	$83.60	8.335%	$90.5681	$90.57	$90.55	$90.60
Purchase #2	$130.46	9.147%	$142.3932	$142.39	$142.40	$142.40
Purchase #3	$249.85	6.107%	$265.1083	$265.11	$265.10	$265.10
Purchase #4	$92.86	8.233%	$100.5052	$100.51	$100.50	$100.50
Purchase #5	$179.34	8.697%	$194.9372	$194.94	$194.95	$194.90
Purchase #6	$201.87	9.800%	$221.6533	$221.65	$221.65	$221.70
Purchase #7	$179.26	9.581%	$196.4349	$196.43	$196.45	$196.40
7 purchase totals =	$1,117.24		$1,211.6002	$1,211.60	$1,211.60	$1,211.60