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	$106.55	13.108%	$120.5166	$120.52	$120.50	$120.50
Purchase #2	$35.95	3.191%	$37.0972	$37.10	$37.10	$37.10
Purchase #3	$221.50	12.687%	$249.6017	$249.60	$249.60	$249.60
Purchase #4	$212.53	12.293%	$238.6563	$238.66	$238.65	$238.70
Purchase #5	$108.56	4.227%	$113.1488	$113.15	$113.15	$113.10
Purchase #6	$190.48	5.232%	$200.4459	$200.45	$200.45	$200.40
Purchase #7	$95.27	13.418%	$108.0533	$108.05	$108.05	$108.10
7 purchase totals =	$970.84		$1,067.5198	$1,067.53	$1,067.50	$1,067.50