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	$44.35	4.856%	$46.5036	$46.50	$46.50	$46.50
Purchase #2	$95.55	11.765%	$106.7915	$106.79	$106.80	$106.80
Purchase #3	$73.59	12.407%	$82.7203	$82.72	$82.70	$82.70
Purchase #4	$80.44	6.595%	$85.745	$85.75	$85.75	$85.70
Purchase #5	$135.38	3.584%	$140.232	$140.23	$140.25	$140.20
Purchase #6	$61.79	7.426%	$66.3785	$66.38	$66.40	$66.40
Purchase #7	$176.55	4.437%	$184.3835	$184.38	$184.40	$184.40
7 purchase totals =	$667.65		$712.7544	$712.75	$712.80	$712.70