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	$250.35	13.865%	$285.061	$285.06	$285.05	$285.10
Purchase #2	$241.43	7.345%	$259.163	$259.16	$259.15	$259.20
Purchase #3	$27.67	10.240%	$30.5034	$30.50	$30.50	$30.50
Purchase #4	$89.80	10.580%	$99.3008	$99.30	$99.30	$99.30
Purchase #5	$6.71	10.667%	$7.4258	$7.43	$7.45	$7.40
Purchase #6	$136.35	7.416%	$146.4617	$146.46	$146.45	$146.50
Purchase #7	$110.35	8.659%	$119.9052	$119.91	$119.90	$119.90
7 purchase totals =	$862.66		$947.8209	$947.82	$947.80	$947.90