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	$235.44	3.159%	$242.8775	$242.88	$242.90	$242.90
Purchase #2	$40.48	4.629%	$42.3538	$42.35	$42.35	$42.40
Purchase #3	$93.65	6.254%	$99.5069	$99.51	$99.50	$99.50
Purchase #4	$133.64	11.417%	$148.8977	$148.90	$148.90	$148.90
Purchase #5	$231.45	9.423%	$253.2595	$253.26	$253.25	$253.30
Purchase #6	$69.88	3.831%	$72.5571	$72.56	$72.55	$72.60
Purchase #7	$92.94	5.275%	$97.8426	$97.84	$97.85	$97.80
7 purchase totals =	$897.48		$957.2951	$957.30	$957.30	$957.40