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	$65.77	8.695%	$71.4887	$71.49	$71.50	$71.50
Purchase #2	$162.48	7.190%	$174.1623	$174.16	$174.15	$174.20
Purchase #3	$226.39	6.560%	$241.2412	$241.24	$241.25	$241.20
Purchase #4	$40.49	7.263%	$43.4308	$43.43	$43.45	$43.40
Purchase #5	$133.81	5.514%	$141.1883	$141.19	$141.20	$141.20
Purchase #6	$228.81	12.537%	$257.4959	$257.50	$257.50	$257.50
Purchase #7	$152.47	12.384%	$171.3519	$171.35	$171.35	$171.40
7 purchase totals =	$1,010.22		$1,100.3591	$1,100.36	$1,100.40	$1,100.40