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	$99.90	5.654%	$105.5483	$105.55	$105.55	$105.50
Purchase #2	$76.51	7.617%	$82.3378	$82.34	$82.35	$82.30
Purchase #3	$47.27	9.271%	$51.6524	$51.65	$51.65	$51.70
Purchase #4	$64.61	5.470%	$68.1442	$68.14	$68.15	$68.10
Purchase #5	$119.91	3.636%	$124.2699	$124.27	$124.25	$124.30
Purchase #6	$54.71	3.337%	$56.5357	$56.54	$56.55	$56.50
Purchase #7	$55.81	13.839%	$63.5335	$63.53	$63.55	$63.50
7 purchase totals =	$518.72		$552.0218	$552.02	$552.05	$551.90