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	$225.48	5.293%	$237.4147	$237.41	$237.40	$237.40
Purchase #2	$235.85	8.716%	$256.4067	$256.41	$256.40	$256.40
Purchase #3	$73.94	11.218%	$82.2346	$82.23	$82.25	$82.20
Purchase #4	$188.86	6.187%	$200.5448	$200.54	$200.55	$200.50
Purchase #5	$87.30	13.231%	$98.8507	$98.85	$98.85	$98.90
Purchase #6	$45.55	10.573%	$50.366	$50.37	$50.35	$50.40
Purchase #7	$65.78	13.399%	$74.5939	$74.59	$74.60	$74.60
7 purchase totals =	$922.76		$1,000.4114	$1,000.40	$1,000.40	$1,000.40