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	$152.96	8.746%	$166.3379	$166.34	$166.35	$166.30
Purchase #2	$241.52	3.578%	$250.1616	$250.16	$250.15	$250.20
Purchase #3	$72.64	5.229%	$76.4383	$76.44	$76.45	$76.40
Purchase #4	$47.39	5.248%	$49.877	$49.88	$49.90	$49.90
Purchase #5	$160.26	4.396%	$167.305	$167.31	$167.30	$167.30
Purchase #6	$84.86	6.576%	$90.4404	$90.44	$90.45	$90.40
Purchase #7	$27.41	12.815%	$30.9226	$30.92	$30.90	$30.90
7 purchase totals =	$787.04		$831.4828	$831.49	$831.50	$831.40