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	$89.42	6.848%	$95.5435	$95.54	$95.55	$95.50
Purchase #2	$91.94	11.727%	$102.7218	$102.72	$102.70	$102.70
Purchase #3	$87.89	3.554%	$91.0136	$91.01	$91.00	$91.00
Purchase #4	$60.83	12.516%	$68.4435	$68.44	$68.45	$68.40
Purchase #5	$105.46	7.740%	$113.6226	$113.62	$113.60	$113.60
Purchase #6	$236.39	9.791%	$259.5349	$259.53	$259.55	$259.50
Purchase #7	$148.38	13.783%	$168.8312	$168.83	$168.85	$168.80
7 purchase totals =	$820.31		$899.7111	$899.69	$899.70	$899.50