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	$76.68	3.178%	$79.1169	$79.12	$79.10	$79.10
Purchase #2	$153.29	6.308%	$162.9595	$162.96	$162.95	$163.00
Purchase #3	$91.62	10.642%	$101.3702	$101.37	$101.35	$101.40
Purchase #4	$79.57	6.624%	$84.8407	$84.84	$84.85	$84.80
Purchase #5	$12.47	3.718%	$12.9336	$12.93	$12.95	$12.90
Purchase #6	$80.29	11.259%	$89.3299	$89.33	$89.35	$89.30
Purchase #7	$120.83	13.410%	$137.0333	$137.03	$137.05	$137.00
7 purchase totals =	$614.75		$667.5841	$667.58	$667.60	$667.50