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	$206.86	4.644%	$216.4666	$216.47	$216.45	$216.50
Purchase #2	$204.53	7.374%	$219.612	$219.61	$219.60	$219.60
Purchase #3	$71.90	8.864%	$78.2732	$78.27	$78.25	$78.30
Purchase #4	$150.50	10.186%	$165.8299	$165.83	$165.85	$165.80
Purchase #5	$17.56	8.312%	$19.0196	$19.02	$19.00	$19.00
Purchase #6	$91.71	13.347%	$103.9505	$103.95	$103.95	$104.00
Purchase #7	$170.58	9.127%	$186.1488	$186.15	$186.15	$186.10
7 purchase totals =	$913.64		$989.3006	$989.30	$989.25	$989.30