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	$24.82	9.486%	$27.1744	$27.17	$27.15	$27.20
Purchase #2	$108.64	7.177%	$116.4371	$116.44	$116.45	$116.40
Purchase #3	$76.37	3.135%	$78.7642	$78.76	$78.75	$78.80
Purchase #4	$32.63	11.394%	$36.3479	$36.35	$36.35	$36.30
Purchase #5	$77.81	11.615%	$86.8476	$86.85	$86.85	$86.80
Purchase #6	$41.41	9.651%	$45.4065	$45.41	$45.40	$45.40
Purchase #7	$119.49	9.840%	$131.2478	$131.25	$131.25	$131.20
7 purchase totals =	$481.17		$522.2255	$522.23	$522.20	$522.10