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	$15.74	3.665%	$16.3169	$16.32	$16.30	$16.30
Purchase #2	$101.83	9.291%	$111.291	$111.29	$111.30	$111.30
Purchase #3	$103.84	10.469%	$114.711	$114.71	$114.70	$114.70
Purchase #4	$15.51	10.488%	$17.1367	$17.14	$17.15	$17.10
Purchase #5	$6.79	10.408%	$7.4967	$7.50	$7.50	$7.50
Purchase #6	$85.38	5.361%	$89.9572	$89.96	$89.95	$90.00
Purchase #7	$82.30	7.319%	$88.3235	$88.32	$88.30	$88.30
7 purchase totals =	$411.39		$445.2330	$445.24	$445.20	$445.20