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	$114.72	12.732%	$129.3262	$129.33	$129.35	$129.30
Purchase #2	$164.53	6.215%	$174.7555	$174.76	$174.75	$174.80
Purchase #3	$15.58	8.359%	$16.8823	$16.88	$16.90	$16.90
Purchase #4	$175.75	11.544%	$196.0386	$196.04	$196.05	$196.00
Purchase #5	$77.94	10.756%	$86.3232	$86.32	$86.30	$86.30
Purchase #6	$20.52	4.677%	$21.4797	$21.48	$21.50	$21.50
Purchase #7	$77.92	7.405%	$83.69	$83.69	$83.70	$83.70
7 purchase totals =	$646.96		$708.4955	$708.50	$708.55	$708.50