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	$14.85	13.767%	$16.8944	$16.89	$16.90	$16.90
Purchase #2	$80.43	3.861%	$83.5354	$83.54	$83.55	$83.50
Purchase #3	$70.65	8.213%	$76.4525	$76.45	$76.45	$76.50
Purchase #4	$172.89	12.220%	$194.0172	$194.02	$194.00	$194.00
Purchase #5	$185.26	13.682%	$210.6073	$210.61	$210.60	$210.60
Purchase #6	$100.72	3.664%	$104.4104	$104.41	$104.40	$104.40
Purchase #7	$173.88	12.748%	$196.0462	$196.05	$196.05	$196.00
7 purchase totals =	$798.68		$881.9634	$881.97	$881.95	$881.90