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	$115.50	6.696%	$123.2339	$123.23	$123.25	$123.20
Purchase #2	$93.43	4.708%	$97.8287	$97.83	$97.85	$97.80
Purchase #3	$196.43	6.169%	$208.5478	$208.55	$208.55	$208.50
Purchase #4	$125.29	8.823%	$136.3443	$136.34	$136.35	$136.30
Purchase #5	$27.45	5.146%	$28.8626	$28.86	$28.85	$28.90
Purchase #6	$125.45	6.137%	$133.1489	$133.15	$133.15	$133.10
Purchase #7	$18.34	9.496%	$20.0816	$20.08	$20.10	$20.10
7 purchase totals =	$701.89		$748.0478	$748.04	$748.10	$747.90