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	$5.79	5.579%	$6.113	$6.11	$6.10	$6.10
Purchase #2	$162.71	13.783%	$185.1363	$185.14	$185.15	$185.10
Purchase #3	$237.84	10.247%	$262.2115	$262.21	$262.20	$262.20
Purchase #4	$160.82	6.866%	$171.8619	$171.86	$171.85	$171.90
Purchase #5	$159.50	13.336%	$180.7709	$180.77	$180.75	$180.80
Purchase #6	$70.89	10.393%	$78.2576	$78.26	$78.25	$78.30
Purchase #7	$244.47	11.871%	$273.491	$273.49	$273.50	$273.50
7 purchase totals =	$1,042.02		$1,157.8422	$1,157.84	$1,157.80	$1,157.90