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	$15.48	13.498%	$17.5695	$17.57	$17.55	$17.60
Purchase #2	$215.69	6.692%	$230.124	$230.12	$230.10	$230.10
Purchase #3	$65.40	9.112%	$71.3592	$71.36	$71.35	$71.40
Purchase #4	$74.48	5.859%	$78.8438	$78.84	$78.85	$78.80
Purchase #5	$89.53	10.351%	$98.7973	$98.80	$98.80	$98.80
Purchase #6	$40.39	4.379%	$42.1587	$42.16	$42.15	$42.20
Purchase #7	$243.84	7.629%	$262.4426	$262.44	$262.45	$262.40
7 purchase totals =	$744.81		$801.2951	$801.29	$801.25	$801.30