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	$28.66	12.633%	$32.2806	$32.28	$32.30	$32.30
Purchase #2	$135.45	9.716%	$148.6103	$148.61	$148.60	$148.60
Purchase #3	$162.45	3.151%	$167.5688	$167.57	$167.55	$167.60
Purchase #4	$206.82	11.638%	$230.8897	$230.89	$230.90	$230.90
Purchase #5	$25.78	13.140%	$29.1675	$29.17	$29.15	$29.20
Purchase #6	$225.99	4.633%	$236.4601	$236.46	$236.45	$236.50
Purchase #7	$196.71	11.562%	$219.4536	$219.45	$219.45	$219.50
7 purchase totals =	$981.86		$1,064.4306	$1,064.43	$1,064.40	$1,064.60