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	$199.85	11.104%	$222.0413	$222.04	$222.05	$222.00
Purchase #2	$20.40	6.210%	$21.6668	$21.67	$21.65	$21.70
Purchase #3	$245.38	3.458%	$253.8652	$253.87	$253.85	$253.90
Purchase #4	$59.40	7.505%	$63.858	$63.86	$63.85	$63.90
Purchase #5	$14.38	6.585%	$15.3269	$15.33	$15.35	$15.30
Purchase #6	$109.52	3.719%	$113.593	$113.59	$113.60	$113.60
Purchase #7	$120.68	8.858%	$131.3698	$131.37	$131.35	$131.40
7 purchase totals =	$769.61		$821.7210	$821.73	$821.70	$821.80