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	$27.80	8.715%	$30.2228	$30.22	$30.20	$30.20
Purchase #2	$236.77	4.262%	$246.8611	$246.86	$246.85	$246.90
Purchase #3	$13.41	8.673%	$14.573	$14.57	$14.55	$14.60
Purchase #4	$169.96	12.367%	$190.979	$190.98	$191.00	$191.00
Purchase #5	$53.91	6.731%	$57.5387	$57.54	$57.55	$57.50
Purchase #6	$34.63	6.680%	$36.9433	$36.94	$36.95	$36.90
Purchase #7	$82.51	9.647%	$90.4697	$90.47	$90.45	$90.50
7 purchase totals =	$618.99		$667.5876	$667.58	$667.55	$667.60