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	$212.27	12.555%	$238.9205	$238.92	$238.90	$238.90
Purchase #2	$109.30	12.789%	$123.2784	$123.28	$123.30	$123.30
Purchase #3	$205.67	12.559%	$231.5001	$231.50	$231.50	$231.50
Purchase #4	$40.79	3.807%	$42.3429	$42.34	$42.35	$42.30
Purchase #5	$77.48	3.587%	$80.2592	$80.26	$80.25	$80.30
Purchase #6	$173.25	6.423%	$184.3778	$184.38	$184.40	$184.40
Purchase #7	$116.50	4.570%	$121.8241	$121.82	$121.80	$121.80
7 purchase totals =	$935.26		$1,022.5030	$1,022.50	$1,022.50	$1,022.50