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	$35.91	13.764%	$40.8527	$40.85	$40.85	$40.90
Purchase #2	$39.98	4.235%	$41.6732	$41.67	$41.65	$41.70
Purchase #3	$208.40	6.341%	$221.6146	$221.61	$221.60	$221.60
Purchase #4	$168.47	6.384%	$179.2251	$179.23	$179.25	$179.20
Purchase #5	$76.78	4.777%	$80.4478	$80.45	$80.45	$80.40
Purchase #6	$131.36	10.256%	$144.8323	$144.83	$144.85	$144.80
Purchase #7	$33.58	11.162%	$37.3282	$37.33	$37.35	$37.30
7 purchase totals =	$694.48		$745.9739	$745.97	$746.00	$745.90