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	$71.99	6.269%	$76.5031	$76.50	$76.50	$76.50
Purchase #2	$104.50	13.355%	$118.456	$118.46	$118.45	$118.50
Purchase #3	$19.67	4.613%	$20.5774	$20.58	$20.60	$20.60
Purchase #4	$101.45	10.821%	$112.4279	$112.43	$112.45	$112.40
Purchase #5	$171.72	7.704%	$184.9493	$184.95	$184.95	$184.90
Purchase #6	$212.46	5.211%	$223.5313	$223.53	$223.55	$223.50
Purchase #7	$230.55	6.507%	$245.5519	$245.55	$245.55	$245.60
7 purchase totals =	$912.34		$981.9969	$982.00	$982.05	$982.00