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	$229.56	8.493%	$249.0565	$249.06	$249.05	$249.10
Purchase #2	$55.79	10.845%	$61.8404	$61.84	$61.85	$61.80
Purchase #3	$129.68	7.748%	$139.7276	$139.73	$139.75	$139.70
Purchase #4	$219.73	8.246%	$237.8489	$237.85	$237.85	$237.80
Purchase #5	$73.37	12.232%	$82.3446	$82.34	$82.35	$82.30
Purchase #6	$25.47	13.377%	$28.8771	$28.88	$28.90	$28.90
Purchase #7	$248.86	10.673%	$275.4208	$275.42	$275.40	$275.40
7 purchase totals =	$982.46		$1,075.1159	$1,075.12	$1,075.15	$1,075.00