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	$7.89	8.110%	$8.5299	$8.53	$8.55	$8.50
Purchase #2	$21.45	3.807%	$22.2666	$22.27	$22.25	$22.30
Purchase #3	$145.51	7.761%	$156.803	$156.80	$156.80	$156.80
Purchase #4	$19.80	10.123%	$21.8044	$21.80	$21.80	$21.80
Purchase #5	$164.94	12.397%	$185.3876	$185.39	$185.40	$185.40
Purchase #6	$153.43	9.272%	$167.656	$167.66	$167.65	$167.70
Purchase #7	$36.57	10.304%	$40.3382	$40.34	$40.35	$40.30
7 purchase totals =	$549.59		$602.7857	$602.79	$602.80	$602.80