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	$36.29	7.648%	$39.0655	$39.07	$39.05	$39.10
Purchase #2	$150.81	11.538%	$168.2105	$168.21	$168.20	$168.20
Purchase #3	$13.54	3.429%	$14.0043	$14.00	$14.00	$14.00
Purchase #4	$69.80	3.826%	$72.4705	$72.47	$72.45	$72.50
Purchase #5	$38.58	7.143%	$41.3358	$41.34	$41.35	$41.30
Purchase #6	$50.93	6.718%	$54.3515	$54.35	$54.35	$54.40
Purchase #7	$188.33	12.451%	$211.779	$211.78	$211.80	$211.80
7 purchase totals =	$548.28		$601.2171	$601.22	$601.20	$601.30