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	$77.99	11.299%	$86.8021	$86.80	$86.80	$86.80
Purchase #2	$131.90	8.300%	$142.8477	$142.85	$142.85	$142.80
Purchase #3	$114.49	3.527%	$118.5281	$118.53	$118.55	$118.50
Purchase #4	$175.47	3.456%	$181.5342	$181.53	$181.55	$181.50
Purchase #5	$31.93	5.710%	$33.7532	$33.75	$33.75	$33.80
Purchase #6	$69.30	5.139%	$72.8613	$72.86	$72.85	$72.90
Purchase #7	$7.97	4.429%	$8.323	$8.32	$8.30	$8.30
7 purchase totals =	$609.05		$644.6496	$644.64	$644.65	$644.60