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	$152.42	9.295%	$166.5874	$166.59	$166.60	$166.60
Purchase #2	$72.97	12.784%	$82.2985	$82.30	$82.30	$82.30
Purchase #3	$148.40	6.817%	$158.5164	$158.52	$158.50	$158.50
Purchase #4	$110.34	6.646%	$117.6732	$117.67	$117.65	$117.70
Purchase #5	$131.33	4.646%	$137.4316	$137.43	$137.45	$137.40
Purchase #6	$139.61	3.213%	$144.0957	$144.10	$144.10	$144.10
Purchase #7	$166.51	3.595%	$172.496	$172.50	$172.50	$172.50
7 purchase totals =	$921.58		$979.0988	$979.11	$979.10	$979.10