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	$121.86	4.239%	$127.0256	$127.03	$127.05	$127.00
Purchase #2	$35.38	12.345%	$39.7477	$39.75	$39.75	$39.70
Purchase #3	$110.29	10.437%	$121.801	$121.80	$121.80	$121.80
Purchase #4	$92.89	4.208%	$96.7988	$96.80	$96.80	$96.80
Purchase #5	$97.32	3.124%	$100.3603	$100.36	$100.35	$100.40
Purchase #6	$249.58	12.132%	$279.859	$279.86	$279.85	$279.90
Purchase #7	$108.77	13.604%	$123.5671	$123.57	$123.55	$123.60
7 purchase totals =	$816.09		$889.1595	$889.17	$889.15	$889.20