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	$12.33	9.252%	$13.4708	$13.47	$13.45	$13.50
Purchase #2	$206.46	8.552%	$224.1165	$224.12	$224.10	$224.10
Purchase #3	$145.72	11.115%	$161.9168	$161.92	$161.90	$161.90
Purchase #4	$128.76	10.762%	$142.6172	$142.62	$142.60	$142.60
Purchase #5	$113.88	12.294%	$127.8804	$127.88	$127.90	$127.90
Purchase #6	$222.81	3.693%	$231.0384	$231.04	$231.05	$231.00
Purchase #7	$81.77	4.656%	$85.5772	$85.58	$85.60	$85.60
7 purchase totals =	$911.73		$986.6173	$986.63	$986.60	$986.60