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	$103.53	7.586%	$111.3838	$111.38	$111.40	$111.40
Purchase #2	$96.90	5.307%	$102.0425	$102.04	$102.05	$102.00
Purchase #3	$78.28	6.243%	$83.167	$83.17	$83.15	$83.20
Purchase #4	$243.46	13.685%	$276.7775	$276.78	$276.80	$276.80
Purchase #5	$148.45	6.390%	$157.936	$157.94	$157.95	$157.90
Purchase #6	$208.39	12.230%	$233.8761	$233.88	$233.90	$233.90
Purchase #7	$60.59	9.434%	$66.3061	$66.31	$66.30	$66.30
7 purchase totals =	$939.60		$1,031.4890	$1,031.50	$1,031.55	$1,031.50