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	$72.26	9.383%	$79.0402	$79.04	$79.05	$79.00
Purchase #2	$99.87	8.147%	$108.0064	$108.01	$108.00	$108.00
Purchase #3	$218.89	10.395%	$241.6436	$241.64	$241.65	$241.60
Purchase #4	$86.48	11.662%	$96.5653	$96.57	$96.55	$96.60
Purchase #5	$182.46	12.783%	$205.7839	$205.78	$205.80	$205.80
Purchase #6	$249.89	6.110%	$265.1583	$265.16	$265.15	$265.20
Purchase #7	$97.32	3.468%	$100.6951	$100.70	$100.70	$100.70
7 purchase totals =	$1,007.17		$1,096.8928	$1,096.90	$1,096.90	$1,096.90