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	$90.47	11.530%	$100.9012	$100.90	$100.90	$100.90
Purchase #2	$76.52	9.187%	$83.5499	$83.55	$83.55	$83.50
Purchase #3	$208.98	13.736%	$237.6855	$237.69	$237.70	$237.70
Purchase #4	$112.91	3.515%	$116.8788	$116.88	$116.90	$116.90
Purchase #5	$18.62	8.792%	$20.2571	$20.26	$20.25	$20.30
Purchase #6	$121.70	5.423%	$128.2998	$128.30	$128.30	$128.30
Purchase #7	$49.66	11.286%	$55.2646	$55.26	$55.25	$55.30
7 purchase totals =	$678.86		$742.8369	$742.84	$742.85	$742.90