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	$48.86	6.453%	$52.0129	$52.01	$52.00	$52.00
Purchase #2	$28.92	8.764%	$31.4545	$31.45	$31.45	$31.50
Purchase #3	$125.88	12.671%	$141.8303	$141.83	$141.85	$141.80
Purchase #4	$14.53	3.378%	$15.0208	$15.02	$15.00	$15.00
Purchase #5	$54.52	4.425%	$56.9325	$56.93	$56.95	$56.90
Purchase #6	$38.55	7.259%	$41.3483	$41.35	$41.35	$41.30
Purchase #7	$228.66	13.404%	$259.3096	$259.31	$259.30	$259.30
7 purchase totals =	$539.92		$597.9089	$597.90	$597.90	$597.80