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	$123.78	12.446%	$139.1857	$139.19	$139.20	$139.20
Purchase #2	$89.55	3.802%	$92.9547	$92.95	$92.95	$93.00
Purchase #3	$126.78	5.739%	$134.0559	$134.06	$134.05	$134.10
Purchase #4	$172.80	13.836%	$196.7086	$196.71	$196.70	$196.70
Purchase #5	$136.44	6.799%	$145.7166	$145.72	$145.70	$145.70
Purchase #6	$137.70	11.411%	$153.4129	$153.41	$153.40	$153.40
Purchase #7	$132.86	10.648%	$147.0069	$147.01	$147.00	$147.00
7 purchase totals =	$919.91		$1,009.0413	$1,009.05	$1,009.00	$1,009.10