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	$199.50	5.735%	$210.9413	$210.94	$210.95	$210.90
Purchase #2	$137.32	10.734%	$152.0599	$152.06	$152.05	$152.10
Purchase #3	$120.68	12.716%	$136.0257	$136.03	$136.05	$136.00
Purchase #4	$112.89	13.657%	$128.3074	$128.31	$128.30	$128.30
Purchase #5	$120.96	5.263%	$127.3261	$127.33	$127.35	$127.30
Purchase #6	$158.64	8.130%	$171.5374	$171.54	$171.55	$171.50
Purchase #7	$61.57	3.130%	$63.4971	$63.50	$63.50	$63.50
7 purchase totals =	$911.56		$989.6949	$989.71	$989.75	$989.60