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	$56.38	7.164%	$60.4191	$60.42	$60.40	$60.40
Purchase #2	$62.98	4.347%	$65.7177	$65.72	$65.70	$65.70
Purchase #3	$70.94	10.344%	$78.278	$78.28	$78.30	$78.30
Purchase #4	$49.47	3.779%	$51.3395	$51.34	$51.35	$51.30
Purchase #5	$150.58	5.365%	$158.6586	$158.66	$158.65	$158.70
Purchase #6	$78.49	6.285%	$83.4231	$83.42	$83.40	$83.40
Purchase #7	$6.80	13.785%	$7.7374	$7.74	$7.75	$7.70
7 purchase totals =	$475.64		$505.5734	$505.58	$505.55	$505.50