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	$19.71	3.824%	$20.4637	$20.46	$20.45	$20.50
Purchase #2	$186.48	10.422%	$205.9149	$205.91	$205.90	$205.90
Purchase #3	$180.40	4.725%	$188.9239	$188.92	$188.90	$188.90
Purchase #4	$42.66	11.825%	$47.7045	$47.70	$47.70	$47.70
Purchase #5	$163.80	6.609%	$174.6255	$174.63	$174.65	$174.60
Purchase #6	$82.61	9.610%	$90.5488	$90.55	$90.55	$90.50
Purchase #7	$83.75	10.292%	$92.3696	$92.37	$92.35	$92.40
7 purchase totals =	$759.41		$820.5509	$820.54	$820.50	$820.50