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	$160.56	12.653%	$180.8757	$180.88	$180.90	$180.90
Purchase #2	$40.56	10.503%	$44.82	$44.82	$44.80	$44.80
Purchase #3	$191.66	8.667%	$208.2712	$208.27	$208.25	$208.30
Purchase #4	$169.43	9.428%	$185.4039	$185.40	$185.40	$185.40
Purchase #5	$30.78	4.562%	$32.1842	$32.18	$32.20	$32.20
Purchase #6	$154.99	7.486%	$166.5926	$166.59	$166.60	$166.60
Purchase #7	$226.49	4.685%	$237.1011	$237.10	$237.10	$237.10
7 purchase totals =	$974.47		$1,055.2487	$1,055.24	$1,055.25	$1,055.30