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	$39.86	7.665%	$42.9153	$42.92	$42.90	$42.90
Purchase #2	$241.68	11.533%	$269.553	$269.55	$269.55	$269.60
Purchase #3	$159.89	5.447%	$168.5992	$168.60	$168.60	$168.60
Purchase #4	$226.88	6.584%	$241.8178	$241.82	$241.80	$241.80
Purchase #5	$90.47	10.242%	$99.7359	$99.74	$99.75	$99.70
Purchase #6	$97.27	6.201%	$103.3017	$103.30	$103.30	$103.30
Purchase #7	$153.30	7.652%	$165.0305	$165.03	$165.05	$165.00
7 purchase totals =	$1,009.35		$1,090.9534	$1,090.96	$1,090.95	$1,090.90