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	$19.91	7.374%	$21.3782	$21.38	$21.40	$21.40
Purchase #2	$18.90	13.345%	$21.4222	$21.42	$21.40	$21.40
Purchase #3	$236.91	11.582%	$264.3489	$264.35	$264.35	$264.30
Purchase #4	$194.80	13.692%	$221.472	$221.47	$221.45	$221.50
Purchase #5	$82.84	11.766%	$92.587	$92.59	$92.60	$92.60
Purchase #6	$62.73	5.797%	$66.3665	$66.37	$66.35	$66.40
Purchase #7	$230.75	6.185%	$245.0219	$245.02	$245.00	$245.00
7 purchase totals =	$846.84		$932.5967	$932.60	$932.55	$932.60