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	$109.66	5.187%	$115.3481	$115.35	$115.35	$115.30
Purchase #2	$131.98	7.336%	$141.6621	$141.66	$141.65	$141.70
Purchase #3	$37.57	12.378%	$42.2204	$42.22	$42.20	$42.20
Purchase #4	$137.69	3.712%	$142.8011	$142.80	$142.80	$142.80
Purchase #5	$111.64	6.541%	$118.9424	$118.94	$118.95	$118.90
Purchase #6	$90.70	11.252%	$100.9056	$100.91	$100.90	$100.90
Purchase #7	$158.39	9.470%	$173.3895	$173.39	$173.40	$173.40
7 purchase totals =	$777.63		$835.2692	$835.27	$835.25	$835.20