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	$35.78	8.256%	$38.734	$38.73	$38.75	$38.70
Purchase #2	$203.65	5.477%	$214.8039	$214.80	$214.80	$214.80
Purchase #3	$80.69	3.414%	$83.4448	$83.44	$83.45	$83.40
Purchase #4	$210.65	3.417%	$217.8479	$217.85	$217.85	$217.80
Purchase #5	$81.84	10.308%	$90.2761	$90.28	$90.30	$90.30
Purchase #6	$87.37	11.505%	$97.4219	$97.42	$97.40	$97.40
Purchase #7	$52.74	12.134%	$59.1395	$59.14	$59.15	$59.10
7 purchase totals =	$752.72		$801.6681	$801.66	$801.70	$801.50