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	$56.87	5.373%	$59.9256	$59.93	$59.95	$59.90
Purchase #2	$166.55	10.709%	$184.3858	$184.39	$184.40	$184.40
Purchase #3	$233.80	8.546%	$253.7805	$253.78	$253.80	$253.80
Purchase #4	$90.44	9.629%	$99.1485	$99.15	$99.15	$99.10
Purchase #5	$130.34	5.271%	$137.2102	$137.21	$137.20	$137.20
Purchase #6	$249.55	3.360%	$257.9349	$257.93	$257.95	$257.90
Purchase #7	$170.27	10.440%	$188.0462	$188.05	$188.05	$188.00
7 purchase totals =	$1,097.82		$1,180.4317	$1,180.44	$1,180.50	$1,180.30