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	$115.55	9.757%	$126.8242	$126.82	$126.80	$126.80
Purchase #2	$238.69	4.258%	$248.8534	$248.85	$248.85	$248.90
Purchase #3	$90.39	4.540%	$94.4937	$94.49	$94.50	$94.50
Purchase #4	$192.84	9.603%	$211.3584	$211.36	$211.35	$211.40
Purchase #5	$43.70	8.330%	$47.3402	$47.34	$47.35	$47.30
Purchase #6	$71.39	12.766%	$80.5036	$80.50	$80.50	$80.50
Purchase #7	$55.37	6.804%	$59.1374	$59.14	$59.15	$59.10
7 purchase totals =	$807.93		$868.5109	$868.50	$868.50	$868.50