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	$75.47	8.502%	$81.8865	$81.89	$81.90	$81.90
Purchase #2	$158.75	12.866%	$179.1748	$179.17	$179.15	$179.20
Purchase #3	$5.42	13.466%	$6.1499	$6.15	$6.15	$6.10
Purchase #4	$178.96	13.735%	$203.5402	$203.54	$203.55	$203.50
Purchase #5	$82.60	3.834%	$85.7669	$85.77	$85.75	$85.80
Purchase #6	$87.90	5.152%	$92.4286	$92.43	$92.45	$92.40
Purchase #7	$128.83	3.192%	$132.9423	$132.94	$132.95	$132.90
7 purchase totals =	$717.93		$781.8892	$781.89	$781.90	$781.80