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	$91.91	12.749%	$103.6276	$103.63	$103.65	$103.60
Purchase #2	$228.95	12.552%	$257.6878	$257.69	$257.70	$257.70
Purchase #3	$141.77	13.210%	$160.4978	$160.50	$160.50	$160.50
Purchase #4	$80.43	6.810%	$85.9073	$85.91	$85.90	$85.90
Purchase #5	$88.54	4.649%	$92.6562	$92.66	$92.65	$92.70
Purchase #6	$92.38	6.609%	$98.4854	$98.49	$98.50	$98.50
Purchase #7	$181.69	10.557%	$200.871	$200.87	$200.85	$200.90
7 purchase totals =	$905.67		$999.7331	$999.75	$999.75	$999.80