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	$52.27	13.821%	$59.4942	$59.49	$59.50	$59.50
Purchase #2	$166.97	12.484%	$187.8145	$187.81	$187.80	$187.80
Purchase #3	$224.82	12.859%	$253.7296	$253.73	$253.75	$253.70
Purchase #4	$72.51	7.859%	$78.2086	$78.21	$78.20	$78.20
Purchase #5	$70.39	7.224%	$75.475	$75.48	$75.50	$75.50
Purchase #6	$229.82	11.432%	$256.093	$256.09	$256.10	$256.10
Purchase #7	$42.75	13.315%	$48.4422	$48.44	$48.45	$48.40
7 purchase totals =	$859.53		$959.2571	$959.25	$959.30	$959.20