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	$52.89	12.387%	$59.4415	$59.44	$59.45	$59.40
Purchase #2	$122.40	6.272%	$130.0769	$130.08	$130.10	$130.10
Purchase #3	$106.86	11.274%	$118.9074	$118.91	$118.90	$118.90
Purchase #4	$12.88	4.520%	$13.4622	$13.46	$13.45	$13.50
Purchase #5	$120.34	6.588%	$128.268	$128.27	$128.25	$128.30
Purchase #6	$205.90	9.728%	$225.93	$225.93	$225.95	$225.90
Purchase #7	$144.69	5.786%	$153.0618	$153.06	$153.05	$153.10
7 purchase totals =	$765.96		$829.1478	$829.15	$829.15	$829.20