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	$75.87	7.684%	$81.6999	$81.70	$81.70	$81.70
Purchase #2	$30.29	3.346%	$31.3035	$31.30	$31.30	$31.30
Purchase #3	$105.46	8.644%	$114.576	$114.58	$114.60	$114.60
Purchase #4	$84.97	4.812%	$89.0588	$89.06	$89.05	$89.10
Purchase #5	$113.75	5.466%	$119.9676	$119.97	$119.95	$120.00
Purchase #6	$183.64	7.183%	$196.8309	$196.83	$196.85	$196.80
Purchase #7	$182.62	4.374%	$190.6078	$190.61	$190.60	$190.60
7 purchase totals =	$776.60		$824.0445	$824.05	$824.05	$824.10