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	$250.72	3.300%	$258.9938	$258.99	$259.00	$259.00
Purchase #2	$57.43	11.243%	$63.8869	$63.89	$63.90	$63.90
Purchase #3	$206.92	13.537%	$234.9308	$234.93	$234.95	$234.90
Purchase #4	$50.25	13.738%	$57.1533	$57.15	$57.15	$57.20
Purchase #5	$29.83	11.766%	$33.3398	$33.34	$33.35	$33.30
Purchase #6	$20.72	4.495%	$21.6514	$21.65	$21.65	$21.70
Purchase #7	$33.39	12.205%	$37.4652	$37.47	$37.45	$37.50
7 purchase totals =	$649.26		$707.4212	$707.42	$707.45	$707.50