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	$91.95	7.111%	$98.4886	$98.49	$98.50	$98.50
Purchase #2	$235.87	3.182%	$243.3754	$243.38	$243.40	$243.40
Purchase #3	$132.60	9.358%	$145.0087	$145.01	$145.00	$145.00
Purchase #4	$211.77	10.672%	$234.3701	$234.37	$234.35	$234.40
Purchase #5	$35.88	12.756%	$40.4569	$40.46	$40.45	$40.50
Purchase #6	$98.65	7.743%	$106.2885	$106.29	$106.30	$106.30
Purchase #7	$249.71	12.142%	$280.0298	$280.03	$280.05	$280.00
7 purchase totals =	$1,056.43		$1,148.0180	$1,148.03	$1,148.05	$1,148.10