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	$106.31	9.234%	$116.1267	$116.13	$116.15	$116.10
Purchase #2	$45.34	8.857%	$49.3558	$49.36	$49.35	$49.40
Purchase #3	$150.92	5.275%	$158.881	$158.88	$158.90	$158.90
Purchase #4	$55.42	10.479%	$61.2275	$61.23	$61.25	$61.20
Purchase #5	$94.69	5.158%	$99.5741	$99.57	$99.55	$99.60
Purchase #6	$156.94	4.769%	$164.4245	$164.42	$164.40	$164.40
Purchase #7	$134.35	9.707%	$147.3914	$147.39	$147.40	$147.40
7 purchase totals =	$743.97		$796.9810	$796.98	$797.00	$797.00