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	$12.92	6.665%	$13.7811	$13.78	$13.80	$13.80
Purchase #2	$151.48	7.226%	$162.4259	$162.43	$162.45	$162.40
Purchase #3	$226.78	6.814%	$242.2328	$242.23	$242.25	$242.20
Purchase #4	$30.86	13.683%	$35.0826	$35.08	$35.10	$35.10
Purchase #5	$104.43	6.533%	$111.2524	$111.25	$111.25	$111.30
Purchase #6	$73.71	8.718%	$80.136	$80.14	$80.15	$80.10
Purchase #7	$170.45	5.840%	$180.4043	$180.40	$180.40	$180.40
7 purchase totals =	$770.63		$825.3151	$825.31	$825.40	$825.30