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	$45.71	4.741%	$47.8771	$47.88	$47.90	$47.90
Purchase #2	$70.65	12.667%	$79.5992	$79.60	$79.60	$79.60
Purchase #3	$141.47	9.680%	$155.1643	$155.16	$155.15	$155.20
Purchase #4	$140.74	10.523%	$155.5501	$155.55	$155.55	$155.60
Purchase #5	$172.98	5.148%	$181.885	$181.89	$181.90	$181.90
Purchase #6	$115.59	10.838%	$128.1176	$128.12	$128.10	$128.10
Purchase #7	$24.65	3.469%	$25.5051	$25.51	$25.50	$25.50
7 purchase totals =	$711.79		$773.6984	$773.71	$773.70	$773.80