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	$70.38	10.355%	$77.6678	$77.67	$77.65	$77.70
Purchase #2	$149.50	10.273%	$164.8581	$164.86	$164.85	$164.90
Purchase #3	$90.56	10.458%	$100.0308	$100.03	$100.05	$100.00
Purchase #4	$72.72	6.337%	$77.3283	$77.33	$77.35	$77.30
Purchase #5	$121.94	4.620%	$127.5736	$127.57	$127.55	$127.60
Purchase #6	$188.76	9.534%	$206.7564	$206.76	$206.75	$206.80
Purchase #7	$44.61	6.832%	$47.6578	$47.66	$47.65	$47.70
7 purchase totals =	$738.47		$801.8728	$801.88	$801.85	$802.00