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	$43.50	13.528%	$49.3847	$49.38	$49.40	$49.40
Purchase #2	$136.59	7.220%	$146.4518	$146.45	$146.45	$146.50
Purchase #3	$72.47	13.785%	$82.46	$82.46	$82.45	$82.50
Purchase #4	$200.82	10.685%	$222.2776	$222.28	$222.30	$222.30
Purchase #5	$39.67	13.604%	$45.0667	$45.07	$45.05	$45.10
Purchase #6	$24.72	10.724%	$27.371	$27.37	$27.35	$27.40
Purchase #7	$54.39	13.141%	$61.5374	$61.54	$61.55	$61.50
7 purchase totals =	$572.16		$634.5492	$634.55	$634.55	$634.70