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	$34.26	9.362%	$37.4674	$37.47	$37.45	$37.50
Purchase #2	$234.33	9.222%	$255.9399	$255.94	$255.95	$255.90
Purchase #3	$116.68	10.169%	$128.5452	$128.55	$128.55	$128.50
Purchase #4	$142.81	12.803%	$161.094	$161.09	$161.10	$161.10
Purchase #5	$82.79	11.624%	$92.4135	$92.41	$92.40	$92.40
Purchase #6	$66.37	11.480%	$73.9893	$73.99	$74.00	$74.00
Purchase #7	$40.37	13.702%	$45.9015	$45.90	$45.90	$45.90
7 purchase totals =	$717.61		$795.3508	$795.35	$795.35	$795.30