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	$210.90	11.684%	$235.5416	$235.54	$235.55	$235.50
Purchase #2	$189.69	4.793%	$198.7818	$198.78	$198.80	$198.80
Purchase #3	$176.31	13.117%	$199.4366	$199.44	$199.45	$199.40
Purchase #4	$108.59	11.212%	$120.7651	$120.77	$120.75	$120.80
Purchase #5	$82.47	9.778%	$90.5339	$90.53	$90.55	$90.50
Purchase #6	$39.69	11.365%	$44.2008	$44.20	$44.20	$44.20
Purchase #7	$96.55	4.358%	$100.7576	$100.76	$100.75	$100.80
7 purchase totals =	$904.20		$990.0174	$990.02	$990.05	$990.00