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	$116.35	13.376%	$131.913	$131.91	$131.90	$131.90
Purchase #2	$248.47	3.547%	$257.2832	$257.28	$257.30	$257.30
Purchase #3	$218.84	5.293%	$230.4232	$230.42	$230.40	$230.40
Purchase #4	$199.87	11.661%	$223.1768	$223.18	$223.20	$223.20
Purchase #5	$224.63	3.145%	$231.6946	$231.69	$231.70	$231.70
Purchase #6	$102.35	10.715%	$113.3168	$113.32	$113.30	$113.30
Purchase #7	$40.31	5.557%	$42.55	$42.55	$42.55	$42.60
7 purchase totals =	$1,150.82		$1,230.3576	$1,230.35	$1,230.35	$1,230.40