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	$238.28	8.863%	$259.3988	$259.40	$259.40	$259.40
Purchase #2	$245.67	5.376%	$258.8772	$258.88	$258.90	$258.90
Purchase #3	$209.29	10.512%	$231.2906	$231.29	$231.30	$231.30
Purchase #4	$204.50	13.726%	$232.5697	$232.57	$232.55	$232.60
Purchase #5	$48.65	9.227%	$53.1389	$53.14	$53.15	$53.10
Purchase #6	$49.30	10.517%	$54.4849	$54.48	$54.50	$54.50
Purchase #7	$38.36	8.243%	$41.522	$41.52	$41.50	$41.50
7 purchase totals =	$1,034.05		$1,131.2821	$1,131.28	$1,131.30	$1,131.30