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	$131.34	6.857%	$140.346	$140.35	$140.35	$140.30
Purchase #2	$133.45	9.636%	$146.3092	$146.31	$146.30	$146.30
Purchase #3	$245.74	10.852%	$272.4077	$272.41	$272.40	$272.40
Purchase #4	$223.45	12.539%	$251.4684	$251.47	$251.45	$251.50
Purchase #5	$73.64	12.398%	$82.7699	$82.77	$82.75	$82.80
Purchase #6	$53.76	6.127%	$57.0539	$57.05	$57.05	$57.10
Purchase #7	$59.53	11.508%	$66.3807	$66.38	$66.40	$66.40
7 purchase totals =	$920.91		$1,016.7358	$1,016.74	$1,016.70	$1,016.80