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	$244.36	10.272%	$269.4607	$269.46	$269.45	$269.50
Purchase #2	$229.76	12.393%	$258.2342	$258.23	$258.25	$258.20
Purchase #3	$202.58	13.118%	$229.1544	$229.15	$229.15	$229.20
Purchase #4	$247.83	4.696%	$259.4681	$259.47	$259.45	$259.50
Purchase #5	$81.95	9.661%	$89.8672	$89.87	$89.85	$89.90
Purchase #6	$217.85	4.622%	$227.919	$227.92	$227.90	$227.90
Purchase #7	$38.25	5.144%	$40.2176	$40.22	$40.20	$40.20
7 purchase totals =	$1,262.58		$1,374.3212	$1,374.32	$1,374.25	$1,374.40