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	$86.58	3.392%	$89.5168	$89.52	$89.50	$89.50
Purchase #2	$128.46	6.496%	$136.8048	$136.80	$136.80	$136.80
Purchase #3	$41.67	3.131%	$42.9747	$42.97	$42.95	$43.00
Purchase #4	$90.79	12.600%	$102.2295	$102.23	$102.25	$102.20
Purchase #5	$240.79	13.824%	$274.0768	$274.08	$274.10	$274.10
Purchase #6	$40.50	6.795%	$43.252	$43.25	$43.25	$43.30
Purchase #7	$90.38	5.235%	$95.1114	$95.11	$95.10	$95.10
7 purchase totals =	$719.17		$783.9660	$783.96	$783.95	$784.00