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	$89.83	8.538%	$97.4997	$97.50	$97.50	$97.50
Purchase #2	$71.88	9.871%	$78.9753	$78.98	$79.00	$79.00
Purchase #3	$216.48	12.217%	$242.9274	$242.93	$242.95	$242.90
Purchase #4	$199.71	12.795%	$225.2629	$225.26	$225.25	$225.30
Purchase #5	$30.48	7.649%	$32.8114	$32.81	$32.80	$32.80
Purchase #6	$187.91	12.191%	$210.8181	$210.82	$210.80	$210.80
Purchase #7	$198.47	6.207%	$210.789	$210.79	$210.80	$210.80
7 purchase totals =	$994.76		$1,099.0838	$1,099.09	$1,099.10	$1,099.10