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	$234.35	9.387%	$256.3484	$256.35	$256.35	$256.30
Purchase #2	$165.32	3.636%	$171.331	$171.33	$171.35	$171.30
Purchase #3	$112.70	9.583%	$123.5	$123.50	$123.50	$123.50
Purchase #4	$5.98	9.639%	$6.5564	$6.56	$6.55	$6.60
Purchase #5	$46.78	8.271%	$50.6492	$50.65	$50.65	$50.60
Purchase #6	$50.72	4.686%	$53.0967	$53.10	$53.10	$53.10
Purchase #7	$177.59	12.804%	$200.3286	$200.33	$200.35	$200.30
7 purchase totals =	$793.44		$861.8103	$861.82	$861.85	$861.70