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	$18.76	8.399%	$20.3357	$20.34	$20.35	$20.30
Purchase #2	$226.65	12.849%	$255.7723	$255.77	$255.75	$255.80
Purchase #3	$46.80	12.375%	$52.5915	$52.59	$52.60	$52.60
Purchase #4	$159.75	9.321%	$174.6403	$174.64	$174.65	$174.60
Purchase #5	$5.40	3.752%	$5.6026	$5.60	$5.60	$5.60
Purchase #6	$137.55	6.767%	$146.858	$146.86	$146.85	$146.90
Purchase #7	$245.58	9.726%	$269.4651	$269.47	$269.45	$269.50
7 purchase totals =	$840.49		$925.2655	$925.27	$925.25	$925.30