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	$224.87	13.804%	$255.9111	$255.91	$255.90	$255.90
Purchase #2	$61.73	13.718%	$70.1981	$70.20	$70.20	$70.20
Purchase #3	$30.72	5.499%	$32.4093	$32.41	$32.40	$32.40
Purchase #4	$162.71	4.594%	$170.1849	$170.18	$170.20	$170.20
Purchase #5	$184.27	6.413%	$196.0872	$196.09	$196.10	$196.10
Purchase #6	$25.34	6.560%	$27.0023	$27.00	$27.00	$27.00
Purchase #7	$27.74	3.853%	$28.8088	$28.81	$28.80	$28.80
7 purchase totals =	$717.38		$780.6017	$780.60	$780.60	$780.60