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	$63.37	4.416%	$66.1684	$66.17	$66.15	$66.20
Purchase #2	$136.61	4.569%	$142.8517	$142.85	$142.85	$142.90
Purchase #3	$194.80	10.825%	$215.8871	$215.89	$215.90	$215.90
Purchase #4	$43.83	8.471%	$47.5428	$47.54	$47.55	$47.50
Purchase #5	$169.50	5.316%	$178.5106	$178.51	$178.50	$178.50
Purchase #6	$112.85	9.414%	$123.4737	$123.47	$123.45	$123.50
Purchase #7	$45.89	6.114%	$48.6957	$48.70	$48.70	$48.70
7 purchase totals =	$766.85		$823.1300	$823.13	$823.10	$823.20