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	$20.48	5.176%	$21.54	$21.54	$21.55	$21.50
Purchase #2	$173.96	12.388%	$195.5102	$195.51	$195.50	$195.50
Purchase #3	$33.64	11.684%	$37.5705	$37.57	$37.55	$37.60
Purchase #4	$240.36	4.198%	$250.4503	$250.45	$250.45	$250.50
Purchase #5	$78.89	5.284%	$83.0585	$83.06	$83.05	$83.10
Purchase #6	$54.79	3.284%	$56.5893	$56.59	$56.60	$56.60
Purchase #7	$89.88	3.281%	$92.829	$92.83	$92.85	$92.80
7 purchase totals =	$692.00		$737.5478	$737.55	$737.55	$737.60