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	$11.63	8.224%	$12.5865	$12.59	$12.60	$12.60
Purchase #2	$200.55	9.659%	$219.9211	$219.92	$219.90	$219.90
Purchase #3	$179.69	11.759%	$200.8197	$200.82	$200.80	$200.80
Purchase #4	$114.71	5.764%	$121.3219	$121.32	$121.30	$121.30
Purchase #5	$103.27	6.490%	$109.9722	$109.97	$109.95	$110.00
Purchase #6	$211.32	8.683%	$229.6689	$229.67	$229.65	$229.70
Purchase #7	$98.65	6.637%	$105.1974	$105.20	$105.20	$105.20
7 purchase totals =	$919.82		$999.4877	$999.49	$999.40	$999.50