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	$160.83	10.813%	$178.2205	$178.22	$178.20	$178.20
Purchase #2	$107.84	5.549%	$113.824	$113.82	$113.80	$113.80
Purchase #3	$103.72	5.248%	$109.1632	$109.16	$109.15	$109.20
Purchase #4	$49.95	11.254%	$55.5714	$55.57	$55.55	$55.60
Purchase #5	$72.80	12.870%	$82.1694	$82.17	$82.15	$82.20
Purchase #6	$59.50	10.182%	$65.5583	$65.56	$65.55	$65.60
Purchase #7	$23.37	13.176%	$26.4492	$26.45	$26.45	$26.40
7 purchase totals =	$578.01		$630.9560	$630.95	$630.85	$631.00