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	$156.87	6.232%	$166.6461	$166.65	$166.65	$166.60
Purchase #2	$129.83	9.632%	$142.3352	$142.34	$142.35	$142.30
Purchase #3	$134.67	4.173%	$140.2898	$140.29	$140.30	$140.30
Purchase #4	$237.45	10.543%	$262.4844	$262.48	$262.50	$262.50
Purchase #5	$95.53	10.409%	$105.4737	$105.47	$105.45	$105.50
Purchase #6	$247.92	10.703%	$274.4549	$274.45	$274.45	$274.50
Purchase #7	$73.86	12.113%	$82.8067	$82.81	$82.80	$82.80
7 purchase totals =	$1,076.13		$1,174.4908	$1,174.49	$1,174.50	$1,174.50