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	$76.29	3.407%	$78.8892	$78.89	$78.90	$78.90
Purchase #2	$61.35	6.351%	$65.2463	$65.25	$65.25	$65.20
Purchase #3	$154.41	12.590%	$173.8502	$173.85	$173.85	$173.90
Purchase #4	$18.38	3.127%	$18.9547	$18.95	$18.95	$19.00
Purchase #5	$238.92	13.570%	$271.3414	$271.34	$271.35	$271.30
Purchase #6	$6.87	7.247%	$7.3679	$7.37	$7.35	$7.40
Purchase #7	$133.41	9.712%	$146.3668	$146.37	$146.35	$146.40
7 purchase totals =	$689.63		$762.0165	$762.02	$762.00	$762.10