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	$7.84	9.729%	$8.6028	$8.60	$8.60	$8.60
Purchase #2	$13.38	12.715%	$15.0813	$15.08	$15.10	$15.10
Purchase #3	$141.31	11.424%	$157.4533	$157.45	$157.45	$157.50
Purchase #4	$83.59	7.235%	$89.6377	$89.64	$89.65	$89.60
Purchase #5	$237.41	11.874%	$265.6001	$265.60	$265.60	$265.60
Purchase #6	$80.67	10.619%	$89.2363	$89.24	$89.25	$89.20
Purchase #7	$78.87	11.822%	$88.194	$88.19	$88.20	$88.20
7 purchase totals =	$643.07		$713.8055	$713.80	$713.85	$713.80