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	$105.89	10.385%	$116.8867	$116.89	$116.90	$116.90
Purchase #2	$81.77	10.593%	$90.4319	$90.43	$90.45	$90.40
Purchase #3	$89.63	7.249%	$96.1273	$96.13	$96.15	$96.10
Purchase #4	$62.78	12.114%	$70.3852	$70.39	$70.40	$70.40
Purchase #5	$51.56	8.476%	$55.9302	$55.93	$55.95	$55.90
Purchase #6	$90.66	6.589%	$96.6336	$96.63	$96.65	$96.60
Purchase #7	$133.56	3.677%	$138.471	$138.47	$138.45	$138.50
7 purchase totals =	$615.85		$664.8659	$664.87	$664.95	$664.80