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	$239.89	6.672%	$255.8955	$255.90	$255.90	$255.90
Purchase #2	$50.97	8.390%	$55.2464	$55.25	$55.25	$55.20
Purchase #3	$110.94	11.161%	$123.322	$123.32	$123.30	$123.30
Purchase #4	$34.60	9.394%	$37.8503	$37.85	$37.85	$37.90
Purchase #5	$81.28	3.124%	$83.8192	$83.82	$83.80	$83.80
Purchase #6	$181.33	4.784%	$190.0048	$190.00	$190.00	$190.00
Purchase #7	$130.50	5.663%	$137.8902	$137.89	$137.90	$137.90
7 purchase totals =	$829.51		$884.0284	$884.03	$884.00	$884.00