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	$163.87	4.734%	$171.6276	$171.63	$171.65	$171.60
Purchase #2	$126.57	5.571%	$133.6212	$133.62	$133.60	$133.60
Purchase #3	$42.39	8.846%	$46.1398	$46.14	$46.15	$46.10
Purchase #4	$129.59	10.197%	$142.8043	$142.80	$142.80	$142.80
Purchase #5	$136.41	11.432%	$152.0044	$152.00	$152.00	$152.00
Purchase #6	$79.50	4.426%	$83.0187	$83.02	$83.00	$83.00
Purchase #7	$83.55	8.182%	$90.3861	$90.39	$90.40	$90.40
7 purchase totals =	$761.88		$819.6021	$819.60	$819.60	$819.50