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	$26.59	4.284%	$27.7291	$27.73	$27.75	$27.70
Purchase #2	$145.64	7.201%	$156.1275	$156.13	$156.15	$156.10
Purchase #3	$49.60	9.304%	$54.2148	$54.21	$54.20	$54.20
Purchase #4	$108.81	7.214%	$116.6596	$116.66	$116.65	$116.70
Purchase #5	$19.88	9.366%	$21.742	$21.74	$21.75	$21.70
Purchase #6	$146.98	12.484%	$165.329	$165.33	$165.35	$165.30
Purchase #7	$112.93	9.744%	$123.9339	$123.93	$123.95	$123.90
7 purchase totals =	$610.43		$665.7359	$665.73	$665.80	$665.60