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	$38.80	12.367%	$43.5984	$43.60	$43.60	$43.60
Purchase #2	$80.55	11.137%	$89.5209	$89.52	$89.50	$89.50
Purchase #3	$237.86	7.865%	$256.5677	$256.57	$256.55	$256.60
Purchase #4	$159.85	9.806%	$175.5249	$175.52	$175.50	$175.50
Purchase #5	$188.33	6.400%	$200.3831	$200.38	$200.40	$200.40
Purchase #6	$75.87	9.649%	$83.1907	$83.19	$83.20	$83.20
Purchase #7	$77.26	4.256%	$80.5482	$80.55	$80.55	$80.50
7 purchase totals =	$858.52		$929.3339	$929.33	$929.30	$929.30