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	$30.94	5.449%	$32.6259	$32.63	$32.65	$32.60
Purchase #2	$98.49	11.262%	$109.5819	$109.58	$109.60	$109.60
Purchase #3	$174.58	12.491%	$196.3868	$196.39	$196.40	$196.40
Purchase #4	$51.76	8.240%	$56.025	$56.03	$56.05	$56.00
Purchase #5	$124.26	10.407%	$137.1917	$137.19	$137.20	$137.20
Purchase #6	$36.30	11.422%	$40.4462	$40.45	$40.45	$40.40
Purchase #7	$206.99	9.700%	$227.068	$227.07	$227.05	$227.10
7 purchase totals =	$723.32		$799.3255	$799.34	$799.40	$799.30