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	$19.96	6.245%	$21.2065	$21.21	$21.20	$21.20
Purchase #2	$42.39	6.462%	$45.1292	$45.13	$45.15	$45.10
Purchase #3	$29.78	13.580%	$33.8241	$33.82	$33.80	$33.80
Purchase #4	$133.59	6.635%	$142.4537	$142.45	$142.45	$142.50
Purchase #5	$225.65	9.628%	$247.3756	$247.38	$247.40	$247.40
Purchase #6	$215.63	12.360%	$242.2819	$242.28	$242.30	$242.30
Purchase #7	$27.61	13.337%	$31.2923	$31.29	$31.30	$31.30
7 purchase totals =	$694.61		$763.5633	$763.56	$763.60	$763.60