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	$238.27	11.164%	$264.8705	$264.87	$264.85	$264.90
Purchase #2	$44.51	3.685%	$46.1502	$46.15	$46.15	$46.20
Purchase #3	$62.60	7.476%	$67.28	$67.28	$67.30	$67.30
Purchase #4	$122.90	13.607%	$139.623	$139.62	$139.60	$139.60
Purchase #5	$50.66	6.556%	$53.9813	$53.98	$54.00	$54.00
Purchase #6	$50.44	4.669%	$52.795	$52.80	$52.80	$52.80
Purchase #7	$28.43	9.454%	$31.1178	$31.12	$31.10	$31.10
7 purchase totals =	$597.81		$655.8178	$655.82	$655.80	$655.90