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	$94.46	9.542%	$103.4734	$103.47	$103.45	$103.50
Purchase #2	$89.76	11.641%	$100.209	$100.21	$100.20	$100.20
Purchase #3	$61.50	11.633%	$68.6543	$68.65	$68.65	$68.70
Purchase #4	$11.89	12.199%	$13.3405	$13.34	$13.35	$13.30
Purchase #5	$60.95	10.310%	$67.2339	$67.23	$67.25	$67.20
Purchase #6	$145.62	8.168%	$157.5142	$157.51	$157.50	$157.50
Purchase #7	$40.54	12.537%	$45.6225	$45.62	$45.60	$45.60
7 purchase totals =	$504.72		$556.0478	$556.03	$556.00	$556.00