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	$36.68	3.310%	$37.8941	$37.89	$37.90	$37.90
Purchase #2	$229.71	12.254%	$257.8587	$257.86	$257.85	$257.90
Purchase #3	$92.59	6.551%	$98.6556	$98.66	$98.65	$98.70
Purchase #4	$119.60	10.335%	$131.9607	$131.96	$131.95	$132.00
Purchase #5	$149.54	7.298%	$160.4534	$160.45	$160.45	$160.50
Purchase #6	$106.53	7.874%	$114.9182	$114.92	$114.90	$114.90
Purchase #7	$195.56	9.651%	$214.4335	$214.43	$214.45	$214.40
7 purchase totals =	$930.21		$1,016.1742	$1,016.17	$1,016.15	$1,016.30