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	$199.71	9.478%	$218.6385	$218.64	$218.65	$218.60
Purchase #2	$139.48	5.157%	$146.673	$146.67	$146.65	$146.70
Purchase #3	$245.98	13.702%	$279.6842	$279.68	$279.70	$279.70
Purchase #4	$187.70	11.508%	$209.3005	$209.30	$209.30	$209.30
Purchase #5	$65.34	3.334%	$67.5184	$67.52	$67.50	$67.50
Purchase #6	$89.27	12.452%	$100.3859	$100.39	$100.40	$100.40
Purchase #7	$230.72	12.213%	$258.8978	$258.90	$258.90	$258.90
7 purchase totals =	$1,158.20		$1,281.0983	$1,281.10	$1,281.10	$1,281.10