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	$135.59	13.660%	$154.1116	$154.11	$154.10	$154.10
Purchase #2	$130.56	8.874%	$142.1459	$142.15	$142.15	$142.10
Purchase #3	$224.78	5.574%	$237.3092	$237.31	$237.30	$237.30
Purchase #4	$75.27	6.839%	$80.4177	$80.42	$80.40	$80.40
Purchase #5	$94.66	10.499%	$104.5984	$104.60	$104.60	$104.60
Purchase #6	$184.39	10.276%	$203.3379	$203.34	$203.35	$203.30
Purchase #7	$37.89	6.658%	$40.4127	$40.41	$40.40	$40.40
7 purchase totals =	$883.14		$962.3334	$962.34	$962.30	$962.20