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	$55.45	10.150%	$61.0782	$61.08	$61.10	$61.10
Purchase #2	$32.76	7.504%	$35.2183	$35.22	$35.20	$35.20
Purchase #3	$69.72	4.502%	$72.8588	$72.86	$72.85	$72.90
Purchase #4	$159.26	10.261%	$175.6017	$175.60	$175.60	$175.60
Purchase #5	$200.63	9.870%	$220.4322	$220.43	$220.45	$220.40
Purchase #6	$168.31	6.223%	$178.7839	$178.78	$178.80	$178.80
Purchase #7	$68.87	13.540%	$78.195	$78.20	$78.20	$78.20
7 purchase totals =	$755.00		$822.1681	$822.17	$822.20	$822.20