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	$137.41	12.695%	$154.8542	$154.85	$154.85	$154.90
Purchase #2	$84.41	7.563%	$90.7939	$90.79	$90.80	$90.80
Purchase #3	$168.92	7.285%	$181.2258	$181.23	$181.25	$181.20
Purchase #4	$138.39	6.165%	$146.9217	$146.92	$146.90	$146.90
Purchase #5	$46.90	7.756%	$50.5376	$50.54	$50.55	$50.50
Purchase #6	$206.87	13.619%	$235.0436	$235.04	$235.05	$235.00
Purchase #7	$94.77	9.223%	$103.5106	$103.51	$103.50	$103.50
7 purchase totals =	$877.67		$962.8874	$962.88	$962.90	$962.80