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	$245.72	10.199%	$270.781	$270.78	$270.80	$270.80
Purchase #2	$9.42	12.113%	$10.561	$10.56	$10.55	$10.60
Purchase #3	$137.37	9.846%	$150.8955	$150.90	$150.90	$150.90
Purchase #4	$201.95	12.701%	$227.5997	$227.60	$227.60	$227.60
Purchase #5	$238.30	7.613%	$256.4418	$256.44	$256.45	$256.40
Purchase #6	$95.83	7.644%	$103.1552	$103.16	$103.15	$103.20
Purchase #7	$240.94	9.162%	$263.0149	$263.01	$263.00	$263.00
7 purchase totals =	$1,169.53		$1,282.4491	$1,282.45	$1,282.45	$1,282.50