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	$108.79	6.189%	$115.523	$115.52	$115.50	$115.50
Purchase #2	$179.29	3.370%	$185.3321	$185.33	$185.35	$185.30
Purchase #3	$55.81	3.811%	$57.9369	$57.94	$57.95	$57.90
Purchase #4	$13.66	10.290%	$15.0656	$15.07	$15.05	$15.10
Purchase #5	$131.67	5.696%	$139.1699	$139.17	$139.15	$139.20
Purchase #6	$148.48	12.734%	$167.3874	$167.39	$167.40	$167.40
Purchase #7	$129.26	7.622%	$139.1122	$139.11	$139.10	$139.10
7 purchase totals =	$766.96		$819.5271	$819.53	$819.50	$819.50