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	$147.94	13.209%	$167.4814	$167.48	$167.50	$167.50
Purchase #2	$139.80	12.643%	$157.4749	$157.47	$157.45	$157.50
Purchase #3	$121.52	13.567%	$138.0066	$138.01	$138.00	$138.00
Purchase #4	$29.80	8.234%	$32.2537	$32.25	$32.25	$32.30
Purchase #5	$197.35	13.411%	$223.8166	$223.82	$223.80	$223.80
Purchase #6	$48.32	8.138%	$52.2523	$52.25	$52.25	$52.30
Purchase #7	$72.68	13.684%	$82.6255	$82.63	$82.65	$82.60
7 purchase totals =	$757.41		$853.9110	$853.91	$853.90	$854.00