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	$38.62	8.168%	$41.7745	$41.77	$41.75	$41.80
Purchase #2	$116.84	12.364%	$131.2861	$131.29	$131.30	$131.30
Purchase #3	$57.34	13.681%	$65.1847	$65.18	$65.20	$65.20
Purchase #4	$189.47	3.821%	$196.7096	$196.71	$196.70	$196.70
Purchase #5	$25.86	13.317%	$29.3038	$29.30	$29.30	$29.30
Purchase #6	$36.52	6.646%	$38.9471	$38.95	$38.95	$38.90
Purchase #7	$61.71	9.388%	$67.5033	$67.50	$67.50	$67.50
7 purchase totals =	$526.36		$570.7091	$570.70	$570.70	$570.70